Sounds like a good idea in principle, but what would prevent it from becoming "stealmyidea.com"?

Ideas are rarely unique anymore. The real question is can you turn a profit? If yes, what hurtles are in place that stopped other people from already doing it? If this site helps gauge the business impact of an idea, great. Sharing the solutions to implement the idea, well that would be silly.

People are inadvertently "stealing" each other's ideas all the time. For example, Seth Godin's idea from yesterday about live presentation construction software for the iPad. I tweeted the same idea during the iPad keynote but there's no way he "stole" it from me. Ideas simultaneously spring up everywhere because we're all having similar/related experiences and our minds aren't that different.

Well, I would not fear that my idea would be stolen, in fact ideas are cheap ( http://www.paulgraham.com/ideas.html )

Remember, execution > idea

CambrianHouse did this for a while and had a very vibrant community. They shut down and became VenCorps because they felt like nothing was actually getting accomplished.