I did this yesterday evening. When I was 99% done my photoshop crashed with an error message and of course I haven't saved cause it was just a speed doodle....I was upset cause I kind of liked how it turned out. So the only thing I could do is to take a screenshot of the little thumbnail in the photoshop navigator and blow it up and paint over it again. That's what I did... ^^
Again some iPhone paintings. I'm testing a new version of "brushes". Now it's even possible to import your paintigns via wifi to your mac and playback the whole painting process at a higher resolution if desired. Another neat feature is that you can export the painting process as a movie file. Check this out!