This is a really neat assignment. I made a search engine to search for fantasy, science fiction & horror:
Really wasn't that hard to do. I can see how useful this is for searching topics. Really similar to Feedster, Technorati, Topix, and Bloglines in many ways, but can be made even more specific as you create an engine specific to what you want to search.
Check out my side bar for my Rollyo button.