It was only with great sadness that I recently dropped support for iOS 3.1.3!!
The first gen iPad will still be stuck on iOS 5, so my next thoughts were to be for iOS 5 and later, but I am open to suggestions. As I have no time right now to be working on an update, I had thought of just making sure it worked ok under iOS 7, and my 3rd gen iPad is running it well on the latest beta of iOS 7. I am hoping to fix up the look-and-feel over the Christmas break (that's the long holiday break in Australia), starting with removing almost all of the XIBs and instead doing things programmatically, which should make updating things to look nicer in iOS 7 MUCH easier.
But, I'm open to thoughts and suggestions!