This is a pretty wierd coincidence, as I just found out about William James Sidis a few days ago (thanks to the yahoodi site) and have been learning a great deal about him since. I put in an inter-library loan request for a copy of Amy Wallace's bio of Sidis; The Prodigy. What this guy did was truly fantastic, although sadly we have probably lost much of his work (that and he was a bit of a nutball.)
Anyway, I have taken many different IQ tests and depending on the ammount of sleep I get and the type of test, my scores have ranged from 116 (on one of those stupid symbol tests) to 168. The vast majority of tests I have taken usually show me to be closer to a high 140's low 150's IQ. It might be genes because my mom was tested at 164 IQ.
I also think it is quite possible that there are a disproportionate ammount of genius-like people on ATOT. First off, there are probably several thousand people checking the threads regularly. Of those, the only people who will post, for the most part, are those who are proud of their IQ score and willing to share. I see this alot. For example I frequent the Princeton Review board and judging from the posts there you would think everyone got a 1450+ and had Ivy League acceptances, however it is human nature to keep quiet on these things unless you can bring something to the table, so to speak.