"In his 1908 essay 'Mathematical Creation,' Poincare insisted that the best way to think about complex problems is to immerse yourself in the problem until you have hit an impasse. Then, when it seems that 'nothing good is accomplished,' you should find a way to distract yourself, 'preferably by going on a walk or a journey'."
-- The New Yorker Magazine, 7.28.08
I tend to go to lunch, a movie, or a pedicure when I need "distractions," though a walk tends to work pretty well, too, and those moments when you're gassing the car and have an aha! moment are pretty common, I find.