Hi Daniel
Yes, I use Photogene on the iPad to do short edits on any photos I upload via the camera kit - and intend to email-on quickly. All my images that I load on to the iPad from the 5D are left in RAW format, and are eventually uploaded to my home iMac for processing as-is. The iPad is good enough to leave photos well alone, and stores them in their original format. I edit local copies on the iPad in Photogene to have a look-see, and find this device somewhat better at showing images in the field than the camera's LCD screen. The only issue I have is that the 5D-II produces 20MB+ files, so Photogene isn't particularly fast. These are large files in anyone's language. I'm keen to see what difference the faster processor in the iPad 2 gives me when I eventually get one - or wait for the iPad 3 (more likely).
ArtStudio is a paint program, not really an image editor as such.