If at least one person is being obnoxious enough to enter completely nonsensical numbers, then probably some people are being less blatantly obnoxious -- e.g., entering plausible but wrong answers (such as their own estimates of their IQ). Not that any poll of this sort is immune to such things.
The latest survey shows that the average LessWronger who entered his SAT or ACT is roughly in the top 0.11%. This is insanely high. For comparison, top 2% can be Mensa members. I do not know the correlation between SAT/ACT and IQ, but I know it's fairly high. Anyway, I'm very curious to see the average score on a real, culture-fair IQ test. Those are the only two tests that are free, online, correct and culture fair, from what I know.
http://www.cerebrals.org/wp/tests/jcti/
http://www.etienne.se/cfnse/
Many people would prefer not to have people knowing their scores. That's great, but please please please do post it anonymously. Especially if it's a low one, but not if it's low because you rushed the test.
JCTI might take a while, so I recommend keeping your answers on Notepad in case you want to leave it and continue later.
Edit: I have included polls, thanks to the commenters.
Post your score here: http://lesswrong.com/r/discussion/lw/fqq/average_iq_on_lw/7yad/