Just personal opinion on the quality of the camera ... and the quality of the images.
I have not read good things about the M8 ... the M9 seems to have corrected the faults of the previous model.
Ok.. I had to ask.. sometimes what people really want to know is info about shooting with a rangefinder and have associated the Leica name to it. Others just want to know about the brand "Leica" itself. What you are asking is a comparison between the m8 and m9.
My experience with the M8 and M9 are that of an evolution not a drastic improvement. The more obvious improvements:
* The biggest improvement... Full frame sensor. From what I can tell, its essentially the same sensor as the M8. Simply larger.
* Improvement on the IR filter (on sensor) to no longer need the IR cut filters (on lens)
* Adjustment of the frame lines to better meet the expectations of shooters familiar with the film M-bodies. (M8's frame lines are "looser"... adjusted for accuracy at close focus)
* Quieter shutter (similar to that of the M8.2) with the 1/4000 top setting (M8 has 1/8000).
* Slight change to the top plate shape.
* No more LCD battery counter on top (bummer)
* No more chrome (bummer); Painted grey or black.
I have read the controversies surrounding the M8 and honestly, I don't really know the hoopla is all about. I won't go into details as I've written about them here before... and yes... this was Leica's first digital rangefinder (first products == guinea pigs). Considering the odds stacked against the company (R&D budget, lack of electronics experience, working within the constraints of an M-body shape/size), I think Leica did fairly well. There isn't a full frame camera out there of the same size.
What I will say is that the M8 has been a complete joy to use and the M9 is following suite just as well. The biggest improvement that impacts me personally, the larger sensor and frame lines. Now the question ... Is it worth the increased premium of the M8? Honestly, I can't really say it is. I was happy with the M8 .. still am. The things that bothered many, don't bother me. The M8 and M9 are just so similar and not without disappointments. I've always been a critic of Leica even though I like their products. I mostly criticize them for their business/design decisions. so here are some points:
* I think its time to REVOLUTIONIZE the M-body rather than just cater to the time old classic lovers. The fact that the m 4/3rds cameras are gaining use from the same crowd is an indication of that fact. Heck.. how hard would it be to get in body IS? The Leica S2 for example is revolutionary... no reason not to be so with this line as well.
* WEATHERPROOFING. How hard can it be to weather proof the M-body and newer lenses?
* Shutter is much improved but I think it can be quieter.
* Battery life could be improved BUT I see the problem... after all they have to work within the confines of the very very very compact M-body shape/size. I think they could improve with extended batteries that integrate into the bottom plate.
* You still have to remove the bottom plate to get to the battery and SD card. BANG HEAD ON WALL.
That's all that comes to mind at the moment. Any more specific questions feel free to ask?
btw... Leica not getting into the m4/3rd movement and coming out with the X1 instead...HUGE mistake in my opinion.. HUGE.