Be careful about this one. Don't freely tell your idea to people who have the wherewithal to then go and build it, because they just might. What Mark Zuckerberg did to the Winklevoss twins should be enough of a cautionary tale for any entrepreneur.
The Winklevoss twins were destined to take their good idea and turn it into crap that Zuckerberg wouldn't want to be involved with and they did eventually turn out a turd.
Very much so. Friendster and MySpace were already prominent.
Zuckerberg got the inspiration to do Facebook from the project the Winklevoss twins were trying to get off the ground, and further to do an elite social network riding off of Harvard. That was their primary contribution to what became Facebook; which is to say, not much.