I also chose 7. Human Random Distribution is probably not very random. I hope that he'll release the data.
I figured 9 had to be the least picked, but I'm starting to think I should have gone with 6...
I've always loved such mind tricks, and I have done this one quite a few times. Before discovering HN, I used to go out a lot, and, when talking to cute girls, I've done this "trick" many times for giggles. Some girls really believed I was a psychic when I got it right :)
Funnily enough, knowing about this trick and the "statistical preference" for the number 7 made me choose 7 in this experiment, without thinking twice about it. I realized this afterward...