Yesterday I read this article in the Science section of the New York Times about daydreaming. It says, basically, that people who let their thoughts wander aren't very happy. This is the kind of study I'm always a little suspicous of: for one thing, they apparently measured happiness by contacting people every 15 minutes or so and asking them to rate how happy they were at that moment. ("Are you happy now?" How 'bout now?") Then they compiled all the yeses and found people were most happy during physical activity, when they brains were basicially turned off. When they had to think and they let their minds wander, they reported themselves as unhappy.
Maybe they should have talked to more writers.
I do sort of understand where this study is coming from. Thoughts can become repetitive, they can chase you around and around and they make excellent attack dogs, hanging on and never letting go until they've convinced you to do something stupid.
But honestly, some of the best moments of my life have been spent daydreaming. When I get blocked writing, my general procedure is to lie down and let my mind wander while I argue the problem out to myself. I can't imagine life without it.