Used to be a pretty awesome way to find new sites tailored to your interests. Later they deleted much of the site content (stumbler blogs and groups) and changed the layout into something less usable. Account deletion hasn't worked for several months.
When I used StumbleUpon the first time, I really fell in love with it. O.k. at the beginning you need some time to understand how it works and that you should have some friends that it is fun, but then it is very easy. Just push the StumbleUpon Button and be surprised what will happening. You can really have a great ride with the StumbleUpon kind of surfing!