Found this at nikonians ....."I use both Leica M series lenses as well as my Nikon gear, and there are places where the Leica lenses excel and places where the differences are not so clear. In my experience, f/8 is the great equalizer, so my favoring the rangefinder lenses is usually at wider apertures. Even when sharpness is equal or better, there are other non-measured aspects, like bokeh. For example, I like my 50mm f/2.0 Leica Summicron at full aperture better than my 50mm f/1.4 or f1.8 AI Nikkors at f/2.0. I think all of the lenses have a similar level of sharpness, but the background blur of the Leica lens is so smooth. Another example is my 35mm lenses from Leica and Nikon. My 35mm f/1.4 Nikkor is sharper at f/2.0 than the Leica is, but the blur of the Nikkor can be very harsh at certain distances. If you were only reading lens tests, some of this would not be revealed. "
PS i think this is something Pentax users have known for a long time
