When I was recently considering signing up for OkCupid, I asked a few friends (actually on a forum, but a small intimate one) about their thoughts on this:

There's still a stigma. That's why people say "there's no stigma anymore!"

(...which is what I was worried about. Of course, "a witty saying proves nothing", but it makes sense -- if there weren't a stigma, there would be less need to defend it against claims that there's still a stigma, and fewer people trying to.)

Okcupid is generally thought of as acceptable as long as you don't take it too seriously. If anyone you know sees you on there, well, they have an account too.

(...which is a pretty good point too. So I took the plunge and joined.)