But it would be useless if you're the first person in your social graph to have a need for particular information; similarly, for it to be very useful you would

But it would be useless if you're the first person in your social graph to have a need for particular information; similarly, for it to be very useful you would want your users to push almost every website they visit into it, or any website which includes useful information (otherwise you would get too many searches filled with junk, or just with nothing). It's also useless if a user doesn't have friends using it (as compared to other programs; see below), and so bootstrapping up would be a bit hard. Essentially, you're talking about something like Chrome's history search (it indexes the content of every page you visit, and allows you to do full-text searches of them), but with the ability to expand the search to other users indexes. You'll want to make it entirely painless for users to add pages - a keyboard shortcut at most - and integrate into the browser as much as possible. It's also probably a good idea to add some mechanism to identify users with reliable indexes and allow others to use them; a karma system could be used for this (add karma if a result is useful, remove it if it's not - similar to how HN works with comments). Users with really low karma (indicating that they're pushing lots of spam sites into the service) would have their results biased against in full-index searches, or outright removed without them being aware (similar to how users on HN can be killed, so that the see all their posts normally but no one else does). Disclaimer: I'm not quite awake, so take this advice with a huge grain of salt. It's just my thoughts on the idea.