Zniff
Zniff.com, now in beta, is a search engine that uses the database that users have created in Spurl. This means that the tags that users have entered are now searchable on a mass scale! The subtitle for the site is "the human search engine" with the line that it is "by humans, for humans."
I ran a couple of searches and found great results. Now all it needs is an RSS feed for changing results of searches. That would be ultimately sweet!