Another way to waste time

I couldn't see what the fuss was about stumbleupon until I tried it. Basically, you tell it what kind of stuff you're into (music, art, technology, etc) and it sends you to a web site it recommends based on your interests. You tell it whether or not you like the site, and its recommendations get better and better. I doubted this last part, until I told it a few sites I liked. Its recommendations were dead-on, and I immediately found incredibly useful sites I hadn't even known existed.