Funnily enough, I've met several. Generally, by the point they get to discussing it online, they've already read all the books in their local library, done online research, possibly taken a few psychology classes and started reading medical journals. Think I'm kidding, you don't know Aspie persistence... Eventually they either decide not to go for diagnosis because they're in a good situation and don't need help; or they'll go and ask a doctor and about three quarters of the time they'll be told, "Yep, you've got some autistic traits there," or even have family tell them, "Actually, you were diagnosed as a kid and we never told you."

It does happen. Tends to happen more often on autism-dedicated forums rather than general psych forums, though.

Perna, if you want to talk to some of the people who are trying to figure out whether they should see doctors because of their autistic traits, I suggest you try going to Wrong Planet; it's an autism web site where we often do get people who suspect they may have a PDD and are trying to get help. At least one every week (it's a very active forum, but that IS often.)
http://www.wrongplanet.net