I have two mostly unused sketchbooks sitting on the floor next to my desk. I doodle in them once in awhile, but it always feels really forced since I'm one of those scumlords who does mostly digital work. (Blame being a lefthanded smudgemaster. Or just lazy.)
When I do warmup sketches on the computer, it usually just ends up being a canvas of squiggles, eyes, and eventually just 'YAY BUTTS' written over everything.