Jason Alba has an interesting post, Living Life 16 Minutes At A Time, where he describes how he managed more in less time since he for a while had to work in 16 minutes sessions.
I find this really interesting, it is sometimes far too easy to lose focus and do something else. With a limited time available for a certain task you have to stay focused.
Since life is not work alone I prefer a mix. Take three serious sessions doing important things and then reward yourself using every forth session for leisure, whatever you feel like doing.
Another thing to remember, work with your email in sessions too. While doing something else, close down your email (all of them). Email is a major distraction, limit it as much as possible.
This was originally posted at another (now extinct) blog of mine.