I've also been experimenting with Rescuetime, with mixed results.

Pros: It makes me more aware of the amount of time I spend procrastinating, and the popup it throws at me after 5 minuates of inactivity can get me back on task if my procrastination takes the form of non-computer stuff.

Cons: I don't feel like I'm procrastinating less, and my efficiency graphs definitely confirm that impression.