If you have an iPad (or iPhone/iPod) and you are looking for a way to burn free time you probably don't have, check into a program called Uzu.
Back in our hippie days, we had a little toy, I can't recall what it was called, but which was essentially a slab of clear plastic with a flexible backing and some kind of oil emulsion under it. You dragged your fingertip along the backing and got a shiny, colored line under the clear covering. You could vary it with pressure, use more than one finger, and create some cool, mind-blowing patterns.
The colors, man, the colors!
Uzu is the electronic counterpart, allowing you to create all manner of interactive foofaraw on the screen. Sucks you right in.
The grandsons had a ball with it yesterday. My son-in-law started playing with it and finally said, "You better take this away now ..."
Warning: Don't give it to anybody who is stoned, because I expect you won't get your device back until the battery dies.
Far out, dude ...