I'm afraid I can't let you do that, Dave.

Oh, this is just about the coolest thing I have found in a long time!

Check out this awesome productivity trick...a tiny file that pops up a reminder every 20 minutes. Lifehacker's How-to Geek explains:

Once the script has been launched, it will ask you every 20 minutes to consider how you are spending your time, and ask you whether you want to continue—answering yes will start the timer over, otherwise the script will exit. At first glance it may sound annoying, but after using this script for a few hours I've already caught myself doing "research" on Wikipedia and goofing off on IM—this reminder is an excellent tool to keep you focused on productivity.

I just set mine up, adapting the message to one that is more meaningful to me (as an attorney, this is a GREAT way to remind yourself to log your time working on cases). Try it--it'll take you two minutes!