I think drawing on the iPhone is a lot of fun and a great way to pass the time or jot down quick ideas. The free app Doodle Buddy goes even further with the ability to connect two iPhones and work together. You can also select a background, like a tic-tac-toe board, which can come in handy. You can draw on top of your own pictures as well.
Related: Changing Desktop Background, Quick Look to iPhoto, iMovie’11 reduce background noise bug, Hard drive full from pictures and music – recommendations?, Blurred images with HDR turned on iPhone 4.

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