I've worked intensively with M9 cameras during about 3 months.
If I had to go on a deserted island and choose one camera (understanding a still camera), I would choose the M over any other gear available, included MF.
Don't get me wrong, I didn't like the handling at all except the left hand because the size of the glasses is just about right. I didn't like very much the dificult focussing in some situations, the position
of the viewfinder and found the size of the body a little too large.
I didn't particularly find this extreme built quality Leica is known for (in the body I refer). It's well built, no doubt, but being used of a 1DMK3 and 4 you don't particularly find a stellar difference, at least I didn't.
There is something different with this camera, the volume of pictures shot is much less while the rate of keepers is higher. That was constant on good or bad days. You can turn the problem up and down, left or right: it's a camera that helps to take better pictures. I suspect that it's because it's simple, non-intrusive and obliged to get more involved into the action. In other words, it's a camera that helps the photographer who is commited with what he-she's doing, and at the same time, very fast in use because it's dead simple. It's very painfull for fashion...in the studio, but, again, outside the studio, in a fashion session in-situ, it can smokes any dslr, without talking of MF.
The pictures taken by the Leica, or lets say in another way, the M allows a freedom in space that result in more dynamic and spontaneous action. It's a collaborative camera. The non-photographers (in short, the people that point the lens, talents included) react differently to a rangefinder and they tend to be more relaxed and let you enter in more intimacy. No other camera does that. A point and shoot, you look amateur voyeur, a dslr, you look distant pro. The M design is just about right. It's trustable.
But...that said #2
When I got the GH2, it was a discovery to me and a big surprise. The day I got the GH2 is the day I decided that I will not buy a M. Before someone jumps on me saying: "what? Are you comparing the GH2 with the M9?"...let me explains my view on that and then you can through your bombs on me if you feel like.
Yes, I will compare to some extend the GH2 to the M. (and I'm not making a mistake with the GF2 that looks more like a rangefinder).
The first time I used the EVF, I was amazed indeed. Now it's normal and Sony already does better EVF. But having all the infos inside, being able to zoom for focusing without having to get the eye away from the viewfinder, this is Leica spirit to me. Filming in live view within the viewfinder, this is M spirit too. Then, the size. The size of the gh2 is the size I'd like the future M generations to have, more or less. Also, the size of the m4/3 lenses are very much on the size of the M lenses. And it's just about perfect.
I found with the GH2 a camera with a similar flavour than the M, yes. It's fast, small, efficient and fun. But, it's electronic is way more advanced.
Then, the Leica M lenses are suiting very well the GH2, although, honestly, I don't find that they increase the IQ, at all.
So, a new generation Leica Rangefinder, but with the electronic of 2011 and video capabilities, then I would reconsider a possible M_ purchase.
Ps: and if an EVF, please, an EVF that display the "hors-champ" (more than 100% but the surrownding).
Answering Michael question: my motivation to reconsider buying a M will not be because of the lens line, because those lenses are adaptable to more modern devices. It would be the body.
As I said, an EVF, maybe also a modular sensor, like Ricoh did, wouldn't be bad (something I'm asking for years), keeping the M spirit.
So shooting rangefinder, yes, but shooting modern, not any more with what's there.
And why not a universal mount, like the M42-M39 in the past ? (After all, I use the M39-M42 with the GH2 and it's great to have so many brands still usable in the 21' century)
With the recent progress of the APS, is it really necessary a FF rangefinder now? I 'm not sure really.
Leica could join a Sony Nex or a m4/3 standard, not kidding. Those are brilliant format in wich tech goes fast and they could benefit R&D. Then, they can apply their own sauce, a less agressive AA, hand-made built, golden components if they feel like, but the point is that they should escape the CCD.
And, oh yeah...video. With everything stabilized and digi ND filters so we don't need any more zacutories. The M should be able to shoot hand-held videos with no hassle. (actually, mobile phones do that now)