I think this is great. A quick download creates a little toolbar on your browser with a "StumbleUpon" button. You click it and it takes you to a random website that you are probably interested in (you set up a checklist of interests in the beginning). Some screen shots and explanations are here. You can go straight to StumbleUpon here.
I messed with a little this morning and I think it is great. Really great. That button just stares at you daring you to push it.