I've had some playtests of a couple designs but nothing past the early prototype stage so far. I often attend a local design group to both get my own designs tested and to test others' designs but I tend to prefer more complex games than the general group.
Speaking of, if you're anywhere near New Jersey, there's a convention in early November that is specifically to match game designers with playtesters. I go every year as a player and see neat stuff. If you ever get to a point where you're
really really going to finish, you might want to take it to this con.
It's called Metatopia and is one of the
4 5 6? conventions run by Double Exposure.