The Waypath Project is worth a visit because they are trying to do two very challenging and cool things. The first is, provide a per-post weblog search, rather than the kind of per-page search you can get on Blogdex or Google. The second is to search things based on similarities in content, rather than just doing keyword matches.
I’m glad to see this: I know Steve (from Waypath) from a prior gig and he’s just half of a dangerously smart team. He’s taken great pains to point out how the Waypath stuff is better (in many ways, scalability not being the least of them) than any of these other new information retrieval techniques. While it may look like query by example, it adds a significant amount of magic to refine the example and thereby deliver better results.