We've been seeing a lot of these idea threads lately. Maybe someone should make an "I have an idea" site :D It would be nice to have a page per idea, plus commenting, and maybe some sections for research (other competitors in the area, probable market sizes, etc). If I had unlimited funds, I always thought it would be cool to start a company that did nothing but churn out little ideas. People could put idea synopses…
Have a look at http://www.halfbakery.com/ - it's pretty much exactly what you describe in terms of an ideas site. Also, there are companies which churn out little ideas - my girlfriend works for one. It's pitched as an innovation consultancy, aimed at opening up new markets for companies big enough to afford their fees. Not sure if that's exactly what you were talking about, but maybe kind of similar?
I mean, it's a good concept of course, but if I'm looking for entrepreneurial web ideas, I have to figure out whether they're in 'business', 'computing', 'culture', etc.
Also, many of those ideas suck, which is fixed easily enough with moderation, but it makes you wonder how many people would have upvoted Twitter or Facebook as an idea? I'm guessing far fewer than use the service, for sure.