ktla.com has an article regarding a pedophile in LA using an online dating site to try to meet single moms with kids (direct violation of his probation). No harm came of it as a child advocacy group was keeping an eye on him and notified authorities. This could have easily happened in any other environment (like bars, etc..) though I feel it is easier to spoof your appearance and profile online. Single Parents have to be so careful these days.
5 Star Online Dating Sites
http://www.5staronlinedatingsites.com/article.php?story=Blog-Dating-Sex-Predators