In the 4 hour work week Tim Ferriss talks about Parkinson's Law. Parkinson's law states that "work expands to fill the time available" which seems to hold true for me. I figure that if I have time to spare I can read RSS feeds for just a little while or check email.
To combat this I have been setting fake deadlines to challenge myself. In the morning I usually have a lot of meeting so setting a deadline of noon to finish things is really challenging, if I finish the task before then it is a lot more rewarding than if I let it swell to the time allotted for it.