For some of us, who are hearing about the word Quora for the first time - Quora was created as Yahoo Q&A done for the Web 2.0 world. You can read more about it at http://www.quora.com/about.
But the reasons I love the service is that i generally come to know stuff about the things i really want to know. For example, what the heck does Olympic medallists do in London after they win the medal. Yeah, the kind of the questions the interviews are supposed to ask from famous personalities. But they never ask. I get those answers at Quora.