Hello Tommy,
being back from Israel / West Bank while my M9 was on (third) maintenance trip to solms, I can confirm that the D700 is clearly not the ideal camera to shoot in "difficult" environments: its body + lens size and loud shutter attracts attention and very often ruins spontaneity.
Wherever I was - Jerusalem, Bethlehem, Ramallah, Hebron, Kalandia, camps, ... - I missed my "stealthed" M9's reduced size, non-existent weight and silent shutter.
D700's autofocus did not help that much, due to its tendency to lock on high contrast patterns as opposed to intended subjects in quick shots, and I missed the ability to see what was going on outside scene framed in the viewfinder (one of the greatest bonuses of rangefinder cameras). Framing people with the 24-70 was like pointing a rocket launcher and made subjects adversely perceive me as a "pro" making money out of their conditions. Even when I switched to the 35mm, things changed not that much since the D700's loud shutter noise was audible up to 10 meters away - lots of turned heads.
In such environments the M9 (with black-taped logos) would had made me look as one the other hundreds "tourists" with compact cameras, i.e. inoffensive by definition.
I can confirm that from the pure image quality standpoint, the M9 is the finest camera I had the opportunity to use south of the D3x and (some) digital medium format systems. Focus is as good as your eye, rangefinder alignment and lens calibration; metering is not as sophisticated as in the D700 but is easy to learn; M lenses are on average quite better than Nikon counterparts (as an example, the 50mm f1.4 G becomes comparable to the Summicron 50mm f2 mkV only at f5.6, corners catching up at f8). You do not get a good lcd, though. But, at the end of the day, shooting with the M9 is quite a deep experience which no other camera (and I really mean "no other") proved so far able to replicate.
On reliability, the M9 can be a a hit and miss. The M9 is entirely built and tuned by hand ("scary" clips available on youtube), it does not have top quality dials and buttons and its rangefinder is made up of mechanical pieces.
There are perfectly working M9's, and M9's which constantly go to Solms for fixing. Rangefinder alignment can be an issue, since "factory tolerances" are somewhat wide and if you expect every lens to be pinpoint sharp at 100% monitor view, prepare for potential disappointment.
On lenses,best for street / environmental photography I mostly use 28mm and 35mm, the latter probably being the best "single" focal length on the M9. A good 50mm (Summicron IV or V) is useful, but I tend to marginally use it compared to the 28 and 35. The 75mm, 90mm and 135mm are quite difficult to focus "on the fly" at the larger apertures, and I use them for "distant landscapes" and portraits.
You would test any used lens on your M9 before buying as to avoid "rangefinder coupling" issues. A lens calibration performed by Leica is in the €150 ($200) range and is best done on your camera, with an average turnaround time of 3 months.
I hope the above did not bore you that much.
Best regards,
M
--
Mauro
http://www.maurobenphoto.com
http://www.flickr.com/photos/mbenphoto