More fun with the iPad

I have been laid up for a few days for reasons that I won't go into, so I have been playing with the Brushes program on the iPad.
This time I took a watercolour sketch that I did some time ago and again used layers. First I used a layer to trace the basic outlines, then I created a new layer to paint on. I went back to the original sketch and used the eye-dropper to find and save about six dominant colours.
I changed the transparency of the original layer and the paint layer so that I could trace through, while leaving the outline layer on top to serve as a guideline. I find that the trickiest part is remembering which layer I am painting on.
I am really not sure how useful this exercise is, beyond just having fun. It does help me to learn the program and allows me to define the "notan" for a future, larger painting that I may do. It also has the advantage of being easy to undertake while sitting in bed feeling sorry for myself. It certainly isn't any quicker than conventional media, in fact by far the reverse.
I have a couple of other drawing apps that I have downloaded (what else is an artist going to do when she finally aquires an iPad?). Over the next few weeks I plan to try them all out and see which one I like best. So far I have found Brushes the easiest to learn but the others may have features that are worth the extra effort. I will keep you posted.
I would be very interested to hear others' opinions, I notice that more and more of you are experimenting with this new medium. Since the Hockney show in London there has been an enormous amount of publicity about iPad painting and I have to admit that I was inspired initially by Hockney when he first started using his iPhone for sketches a couple of years ago. I am not a big cell-phone user and couldn't justify the expense at that time, but finally decided that the iPad offered enough advantages that I may be able to claim it as a business tool. So here I am.