RescueTime is a little app available for Windows and Mac that basically tracks what sites you go to, or rather, which sites you open and actually use, and how long you’re there. A little creepy, I suppose, but they promise privacy and all that.
I could see this as a great way to realize how much time you spend on the Internet, and it looks like they can even break it down: 5 hours spent on blogs, 6 hours at Wikipedia, 15 hours on email (and that’s just so far this morning.) It’s too bad it’s a stand alone application, though. I would probably use this for sure if it were a Firefox plugin or Greasemonkey script.