I've had days where I didn't do anything the whole day. It doesn't always satisfy me, but I think the defragmentation analogy fits right in there, your mind and body need some rest too every now and then.
On the other hand, when I just push myself to do something, like cleaning something up, I often end up cleaning the whole house.
I guess that works like the upward spiral Steve once talked about, the first, small, accomplishment that you forced upon yourself motivates you to go on with it, it energizes you, and after you've done that next task, you have even more energy, well, mentally anyway. And then at the end of the day you're totally exhausted but hey, you did clean the whole house, sort out those stacks of paperwork, and sunlight once again shines thru your window, not at it.