I will tell you right from the start. This is one of the best (if not the best) camera I've ever laid my hands on. It's fast, it's well build and the exposure and focus is always spot on. This is a pro camera - no doubt about it - it's heavy and I dare to say it has the best design I've ever seen.
This camera was meant to compete with the likes of Nikon F4 or the Canon EOS-1but unfortunately it did not do so well. There are plenty of theories out there as to why this happened and I am going to stir in one more. Some say that it was the lack of a build in flash that cost Minolta good sales but this is certainly not the case as neither F4 or the EOS-1 had one. Another very popular theory says that the 9xi didn't do so well was due to it's awkward user interface - and that is true to some point but the EOS-1 had a similar interface, with most functions hidden under a compartment door and so did the Pentax Z-1p which sold well actually. And let's not forget that 7xi had the same interface which also sold well. My view is that what actually lead to the 9xi's poor sales had to do with Minolta's selling strategy. I mean, back in 1991 the 9xi was $800 more expensive than the 7xi having the same AF and metering module but at the same time less features. A few months later Canon released the EOS-5 and Nikon the F-90 which made the 9xi look outdated in a sense. So minolta had to respond to this by releasing the 700si which was marketed as the more advanced Minolta up to date and it was very favourably priced too, leading to better sales than it's bigger sibling. By 1994 Canon introduced the EOS-1N and by 1996 Nikon released the F-5 which meant that minolta was already on the drawing board for the next 9-series.
But this of course doesn't mean a thing. The 9xi is a fantastic tool even by today's standards.The body is made out of glass fibre-reinforced polycarbonate, with the bottom part and the mirror box being made of zinc and die-cast stainless steel. The lens mount is made out of oil-impregnated sintered stainless steel to reduce friction and a UV-hardened polymer covers areas of Dynax 9xi's outermost surface. And innovations do not stop there. The most important feature of this camera is of course the shutter - and forget about the crappy 1/12.000 sec high speed - you cannot use it anyway because of the reciprocity error occurring above 1/10.000 sec. What is more important is the complete lack of vibrations due to the low weight of the shutter blades and the shortest black-out time (with speeds above 1/60) I've ever experienced - the viewfinder is not blacking out almost at all. I've taken pics with 1/10 (at 28mm) and the results are more than acceptable. How is that done? Well, in order to reach the speed of 1/12.000 sec you need a super-light shutter that can accelerate and stop with minimal vibrations. This is done by replacing 8 out of the 10 shutter blades with carbon-fibre reinforced epoxy material. According to Minolta
"this strong light-weight material allows the blades to withstand the force of repeated firing at high speeds and reduces vibration. And an extremely efficient, compact core-less motor provides the high torque and high speed needed to cock the shutter and return the mirror rapidly between exposures. This enables 9xi's AF system to resume tracking sooner after an exposure is made". And this brings us to another great feature of this camera. The 4.5 frames per second motordrive. This might not sound impressive - EOS 10 had already 5 frames/sec and the F-4s had 5.3. But these speeds were able on focus priority mode, on continuous focusing the speed drops below 3.5 frames per second on both EOS-10 and F-4s (and EOS-5 too) while the 9xi is still able to shoot with a whooping 4.5 frames per second. And this is why there is so short black-out time with this camera, the mirror mechanism is designed to return faster than other cameras.

So what's the catch? The user interface. There is nothing sort of obvious on this camera - you really need to give the manual a couple of good reads. Most of the important camera functions are controlled by the FUNC button and the two dials. There are also some buttons hidden away behind a door compartment a-la EOS-1 (Rewind, quick button (more later), self timer/drive, ISO, Expansion Card). So, how does it work? If you turn the front control dial without pressing the Func button you gain access to shutter speeds in P mode (called Ps), if you turn the rear dial you change in P mode (called Pa). If you press once the Func button and you turn the front dial you change the exposure mode (aperture/speed priotrity), turn the rear dial and you change the exposure compensation. You press the Func button twice and with the front dial you change the AF spots, with the rear the metering mode. Once you do it a couple of times you get used to it and it is always displayed on the panel and the viewfinder but if it is the first time you pick up the camera, you'll probably spend hours trying to switch to A-mode. Things get better once you start using the Quick button, that is a button that you can assign a function to (metering, bracketing, AF spots etc..). I have assigned the AF spots and makes my life so much easier.
Another great feature that is hidden away is the release priority. The camera come on focus priority (the camera will not take a picture until it focuses first). To switch to release priority turn off the camera, open the compartment door and while pressing the self timer button you switch one the camera. Yea... you really need to read the manual....
The viewfinder on the 9xi is a bit darker than other cameras and that is because of a transparent LCD panel that projects information on the viewfinder, such as Func properties, AF area (changes according to the number of sensors you've selected and the orientation of the camera) but it is not a big deal, it is still bright enough and crisp.
And now a few things about the AF. When released, the 9xi was supposed to be the fasted camera in the world. But the next generation cameras (e.g. EOS-5) focused faster with USM lenses than the 9xi. You will find many comments on the internet about 9xi focusing slowly (or not at all). I have tested the 9xi along with the Dynax 5 and I really strangle to see any difference in good light. Even more, the Dynax 5 might start hunting due to the 7 sensors (see my complain on the EOS-300v) while the 9xi with fewer sensors focuses faster and without problems. Where I do see some improvement is in low light conditions where there is less hunting from the Dynax 5 than the 9xi. Anyway, definitely not up there with the EOS series but I cannot complain either - it is better than the EOS-10 if you ask me. Long story, short. Very good AF even by today's standards.
(* Update 24/8/11)
Just to clarify something. AF speed depends greatly on the lens you are using. With the 28-100 f/3.5-5.6 from the Dynax 5, the camera focuses almost as fast as the 5. The problem is with the old 28-80 f/4-5.6 which is slooooow... If you are going to get the 9xi, get it with a lens from the xi-series that was sold with (or newer).
The 9xi does not support custom functions without the silly expansion cards. And what is more annoying, these functions are on the camera, not on the card, the card acts as a key that gives access to these functions. That was a great way for Minolta to milk the cows (consumers to you and me), especially if you think that Canon had been offering custom functions since the first EOS-1.
The 9xi was one of the first cameras which used the so called "fuzzy logic", that is computer programming to understand what subject you are photographing and adjust exposure. It works great but the problem is that it is quite common that sometimes the program freezes - a "help" is being displayed on the panel and you have to switch off and then back on the camera (reboot).
One last thing, the 9xi is sealed against dust and moisture making the camera the most weather-sealed minolta ever produced.
What i would like to see in this camera? The custom functions being on the camera rather on the custom function card. I would love to be able to leave the film lead off the canister or to be able to switch off the eye start feature.
Conclusion
With the exception of the expansion cards, Minolta did not cut corners with this camera. It is a pro tool that unfortunately did not sell as it should. It goes for around £80 in good condition, expect to pay around £120 for one in excellent condition. Money well spend if you ask me, this is a fantastic camera and worth every penny. Consider it one of the absolute bargains of the photographic word. I love mine so much that I bought a non-functioning one for £10 just to have spare parts once they start to get scarce.
Highly recommended - shares the top place of my favourite SLRs together with the EOS-5 (and maybe beats it).
(Update 10/3/12)
I've been using the Minolta 9xi for almost 8 months now and my general impressions remain very good. There are 3 things that came up as issues though.
The first is the AF. As I said previously, there is no point in getting this camera with an old lens. My 28-80 f/4-5.6 is so slow and hunts all the time that eventually compromises the camera's performance. I am after a nice 50 f/1.7 but they seem to be a bit on the expensive side. A good friend was kind enough to let me use his for a while - the viewfinder was so much brighter and the AF speed was as fast as EOS 5's with the EF 50 f/1.8.
Another thing that you might need to consider is getting a custom function expansion card. The eye-start feature consumes so much battery that eventually it will be cheaper for you to buy the card rather than change batteries every 5-6 films. Be careful though, there are many custom function cards from the 7000i/8000i cameras. These WILL NOT WORK! you need the ones that have the "xi" written on them.
The last one - although it's not really an issue- has to do with the camera's interface. Eventually you do get used to it and not only that but you can change between functions just by using your thumb and index fingers only, nothing else. Still, the interface remains complicated though, so many functions are hidden away without you knowing it. Recently I discovered a very useful feature for portrait or landscape photography. It has to do with the use of exposure lock in spot metering mode. Once you take a reading using the exposure lock button and then recompose, you will notice that an exposure graph will appear on the bottom of the viewfinder and show you the difference in exposure between the initial and the final reading. For example, you want to take a picture of landscape - you meter the ground and lock the exposure. If you meter then the sky, the graph will show, for example +2. It means that between the ground and the sky there is 2 stops difference. Great feature but there is just a small mention on the manual and it's not easy to come across.
(Update 30/4/12)
Another update with a secret feature this time. If you press the P button and switch on the camera at the same time, then next time you will try to focus, the camera will display the sensor that it is focusing with. This useful feature is not in the manual !!!