I've had a Novoflex adapter for C/Y lenses to my NEX 5 for several months now and could not be happier. Has worked without any really bothersome issues with every C/Y lens I own (5 or 6 including the early 60mm macro which I had heard could be a problem, and the 100-300 vario sonnar). Lens will focus slightly past infinity so one needs to be mindful of that. There is a very, very slight amount of play right to left once lens is attached, but nothing fore and aft and this has had no effect on image quality.
I've also got a Voigtlander adapter for my Nikon lenses and it has been all I could have asked for as well.
"You pay, you get" as my dad used to say.
Hope this helps.