In the last two weeks I've started to use questions and answer site Quora more or less everyday. Both from my desktop and mobile phone, i.e. the site is quite addictive. It's also one of few new web sites that I feel is raising the bar for all online services (not surprising given the founders Facebook heritage).
Quora might only be Yahoo! Answers for the Silicon Valley (and wannabe Silicon Valley) crowd, but for this crowd the company has created something very interesting. If Facebook is about the social graph, Quora is more like a Facebook application in the sense that it uses the social graph and real identities to create something interesting.
Examples of questions on the site:
Which Nordic Internet startups are doing more than $10m in revenue?
How does Spotify split its contribution to artists?
How did AOL make the decision to go to an all-you-can-eat pricing strategy?
As interesting as the questions are, I find the answers and the people who are answering to be the main driver of value. The site really has managed to get a lot of startup people to be active on the site.
You can check out my Quora profile to get a sense of what a profile looks like and what a user can end up doing on the site.