Maybe I've been lucky, but I bought a second hand Leica M9 around 4 years ago and, except for the rangefinder going out of alignment after I dropped the camera, I have had ZERO problems with the camera. I have received a TON of pleasure, and great quality photos, from the camera.
For me, getting the M9 was a no-brainer because I have been a long-time Leica M film body user, and I already owned perhaps 10 lenses for my M3 and M4-P bodies. I love the simplicity of the M9, all other digital cameras I have used have too many controls and options for my taste. And for quick moving subjects, for me, no autofocus works as well as manual focusing with the rangefinder.
But I am a little old-fashioned, and also a little old.