The NEX-3 I own is much smaller than my dSLR (a Nikon D200) and surpasses it in image quality by a considerable margin (noise, resolution, DR). Of course the NEX is small and is not as intuitive to use as the Nikon and doesn't have the robustness the D200 has. However, for my style of photography, the NEX is much better suited. Smaller, lighter, much more inconspicuous.
I actually have the Novoflex Leica M to NEX adapter right in front of me, and I will try it out tonight. I can already report that the Nikon F to NEX adapter works fine, and the big bonus is, it works well with non-Ai, AI, AF, and AF-G lenses, both full frame and DX!
Sony has stated that they are surprised how many legacy lenses are used on the NEX, but if you see how well integrated this functionality is in the NEX design you might wonder why...
I do not have anything 'worthwhile' to show yet, but when I have shot some nice B/W with my DR 'cron on the NEX, I'll get back to you...