Coding is therapeutic especially when you don't have to do it. Besides, its an easy way to enter flow.
"The hallmark of flow is a feeling of spontaneous joy, even rapture, while performing a task." http://en.wikipedia.org/wiki/Flow_%28psychology%29
Doing some coding during the weekends make me relax (and angry if I cant fix stupid bugs :P). It makes me totally forget the other stuff so that I can start freshly again on monday.