Tell HN: Wikipedia categories rock

Might be an old hat for most HN users, but I only disovered the wikipedia categories recently. Example for movies: http://en.wikipedia.org/w/index.php?title=Category:English-language_films&from=O I suspect this could already be better than imdb (I am probably the last person to still use imdb, too, since I didn't keep up with newer pages). Also, the data from categories might come in really handy for seeding all sorts of specialized web services. Not being an experienced Wikipedia user, I found it a bit non-obvious how to add categories to existing categories.