Sharing ideas. Not exactly a new idea, but I kind of like the interface on this. In their own words:
"Thoughtpile is an open invitation to share your best ideas with the world."
Basically, they come up with a topic, and you come up with answers. Then people can vote on them. You know, like Yahoo! Answers...but a lot prettier. Plus you get to win stuff if your answer gets the most votes at the end of the week (specifically a Herman Miller Embody chair. yes, this is a ploy to sell stuff).
So go ahead, jump into the Thoughtpile.