About a year ago the AI site was launched and closed after a short few days.
http://area51.stackexchange.com/proposals/6607/artificial-intelligence
I'd say the general reason is that we simply didn't draw the right crowd, and there were not enough people asking questions because they weren't working with it but simply said "Wow, AI is cool stuff, I can ask metaphysics questions there!"
However, it may be worth keeping an eye on a few things to consider re-launching the site (and that's what I'd like to discuss).
The Stanford AI Class may have a high volume of people (100k+), I'm doubtful that all of them truthfully understand the complexity of what the course is about, but it's generating some cool interest, and spreading learning.
Already there's three Q/A sites dedicated to a course on AI.
http://www.quora.com/Stanford-AI-Class
http://www.reddit.com/r/aiclass
Would it make sense to resurrect the dead project? Would it just fail again?
Considerations are of course, this interest level may be a one-hit-wonder, and the interest is specific to the class, perhaps not general AI.
Is it too soon? What would be an indication that it's worthwhile to re-launch the site proposal?