I use a Vivitar lens (70-210) and adapter with my NEX sometimes. I like it, it makes me feel like I'm actually "doing" photography as opposed to the kit lens where I feel I have a glorified point and shoot. (that's not what I really think but it is how I feel, if that makes sense). I also use the adapter for a canon 35-70 lens which I just love. That's what I use the vast majority of the time.
Others have already posted about these types of set ups - I think the latest thread was something like "bang for the buck" with a funky wee retro lens.