Such websites do work, but you have to find the right one. A female co-worker of mine in her mid-20s has been going out with her boyfriend for two years, and they live together now. They met using LavaLife.
The problem with some websites for me, at least where I live, is that they have no shortage of Americans, but very few Canadians. I've had girls from Ohio and Michigan contact me and show good interest, but they're all too far away for me. I can't see myself starting a relationship with someone who is a six-hour drive away. (As the crow flies they don't live far away, but due to the Great Lakes one must drive for hours just to get to the other side of Lake Ontario or Lake Erie.) LavaLife seems to be one of the few sites that have a lot of Canadians.
So far on Aspie Affection, there are four girls in my age group - three Americans (one being Carla), and an Aussie (PhoenixKitten).