I'm planning on getting a Slate (HP's offering) probably. While the iPad will benefit from a port of Adobe's camera editing app from the iPhone version, it's the complete lack of an SD card slot or a USB port that kills it for me.
These tablets don't have powerful processors or large amounts of memory, so it's basically going to be a preview device for me. Small and light enough to bring with me, and I can pop in a card or a direct cord and preview. I know a lot of people find the LCD on the camera satisfactory for this, but I can't tell you how often a pictures looks great on the LCD and then comes out with something I don't like. Admittedly, a lot of that could likely be inexperience on my part, but I'm looking forward to a way to preview on a larger screen.
Add that to the ability to run elements or gimp or PSP, and the variants running windows 7 should be the obvious choices vs. the iPad. The iPad is highly specialized towards serving up media, and it will be good at that job. Apple has demonstrated time and again their skill at filling a wanted role. However, that role in this case is not photographers.
Mel