My current favorite way of idling away a few minutes is to try and 'paint' something on the iPhone. I've had the Brushes app installed for ages, but it's only recently that I've tried to actually use it.
I'm pretty hopeless as an artist, as you can tell from the three examples below, but something about it is fun. In many ways, this is harking back to the early days of Windows 3.1, where Paintbrush (one of the few applications that came pre-installed) was something you toyed with when you weren't playing Solitaire.
There's something different about it on the iPhone though - using a finger gives you permission for it to be a bit messy, whereas a mouse and cursor makes you feel that it should be more precise.
The hard thing about painting on the iPhone is that the small screen size means you have to keep zooming in and zooming out in order to switch between detailed lines and broad strokes.
So this is why I need an iPad. Right?