I installed this firefox add-on yesterday, it tracks your time on various sites and you can set it up to warn you if you spend too long on certain sites depending on how you categorise them. I think this is a very good idea!

i'm going to start using it properly next week, but it tells me i've spent around 1½hours on DiS today, 20 minutes on each of google, flickr & the bbc.

hopefully this will help me kill my internet procrastination at work.