Tim Bray has been running series on search that I’ve finally gotten around to reading. Nice series — gives a basic tour of the technology, the hard problems, and one person’s opinions on what works and doesn’t.
I especially liked his article on Metadata. Whether it’s Yahoo’s directory or Google’s PageRank, metadata is what really makes the difference on results. Metadata is hard to come by, so you should take every chance you get to collect it. But don’t expect it to come cheap and don’t expect your users to create it just for you.