Like most twenty-somethings, I've logged many hours surfing YouTube (never on company time, of course). Watching episodes of "You Can't Do That On Television," old music videos, and various home movies of people falling down. What's great about YouTube is that you don't need to be looking for anything in particular to be entertained for hours - just click around and follow responses to other videos.
My district does block access to YouTube from the school's computers, but I've learned how to download the Flash video files that YouTube uses and convert them to a usable mpeg for viewing on other machines. It's a pain, but it gets the job done in a pinch.