I used my iPad a lot this weekend to review and process some RAWs off my 5D2, and my conclusion is that it is NOT yet really worth it.
There is no ACR for iPad, so the fact you shoot in RAW makes no difference, as you can only alter the same things you could if shot in Jpeg (basic things like brightness, saturation, contrast etc).
The preview is very low quality, I dont know why... the file size is right at around 28MB for a RAW file, but the quality is very poor when viewed - cant figure out why, but it is, try zooming to 100% for instance and it is massively blocky and low-quality... whereas the shot is sharp when viewed on a PC monitor (I'd put the quality at something like when zooming to around 400% on a PC monitor, its THAT bad!)
The iPad screen colour profile is completely unique, and photos processed on an iPad and then uploaded to FaceBook, Flickr, or even emailed to a PC will look NOTHING LIKE they do on your iPad screen. For this reason alone, I would never process another photo on an iPad.
There are other reasons, but for me, the iPad doesnt have its place (yet) for processing photos, especially RAWs.
For displaying photos that have been processed on a PC/Laptop and then sent to the iPad it is wonderful - and acts as a very good mobile portfolio.