What I would really like is a little bit like this but not quite the same: full text search over everything I have ever seen on the computer. It would read and index the emails, web pages, word docs, etc as I open them, then later when I think "I know I saw a doc about cache oblivious algorithms", I can search for it without being distracted by 100K documents I haven't seen. Or I can find that email I read, without finding the same phrase in a bunch of junk mail I never opened.
Does anything remotely similar exist?