This looks like an interesting place to follow discussions about search.

So, this is one of the hard problems (You could probably get away with saying that it's the hard problem) in search: what is a reliable measure of the aboutness of a page, given a query? I don't think there's any one answer to this question. I think it would be difficult to come up with a measure of aboutness that would scale well from collections of 10,000 emails to collections of 8,058,044,651 web pages. [Steve Green's Weblog : Weblog]