Michael Reichmann reviews The Leica M9 in Paris:
A Nikon D3x or a Canon 1Ds MKIII can be used as a point and shoot. For all of their sophistication and complexity, with these and similar cameras one can completely remove oneself from the process and just press the shutter.
With an M9 that is not the case. Because it is resolutely manual focus the camera demands that you become involved in the photographic process. This is another aspect of the Zen of Leica M Photography. There's no slacking off. There's no fully auto-everything mode. You must at least manually choose an aperture and you must always focus by eye.
A lengthy yet insightful review worth reading if interested in Leica M cameras in general and the M9 in special.