Topic-Based Aggregators

I came across The Harry Potter Automatic News Aggregator, which made me think if topic-based aggregators are the way of the future. It is a point also made briefly by Ted Leung, who says: “There’s a role here for topics and categories. People have been talking about topical weblogs but I’m not sure I’m ready to go that far. I am more than happy to have topical aggregators like JavaBlogs or SeaBlogs, etc. where I can go to trawl for new bits.”