I've been experimenting using the iPad as a backup device, and for most raw files the iPad can read and display them. getting image files onto the iPad isn't too challenging with the Camera Connection Kit. SDHC cards use the one adaptor, and for CF cards my cheap Belkin USB card reader plugged into the USB adaptor works just fine.
The iPad will import and display nearly every raw format out there (those supported by the OS which means those supported by Aperture). Unfortunately PhaseOne files are not supported.
However, if you have the Phase back set up to use the .TIF extension instead of the .IIQ extension, the iPad does recognize them and allow you to import them as image files. You can see a thumbnail of the image in the import screen, but only a generic icon after that (no image).
You can either use iPhoto to pull them off the iPad and then move them to a folder location of your choice to open them in C1, or in my case Lightroom will allow you to import the files directly from the iPad much like a CF card. Lightroom doesn't display a preview of the images in the import dialog, but after importing I verified the files are copies of the original raws including filenames, and lightroom will build the previews.
One caveat so far is there is no good way to organize the files, other than allow lightroom to separate them into subfolders based on date.
For dSLR shooters who shoot Jpeg+Raw the iPad supports this very well, it only shows one image with jpeg+raw displayed when importing and in the photo app, but when you pull them off of the ipad through lightroom both files get copied.
Too soon to say how useful this is, but all of this functionality requires no 3rd party support. I couldn't get C1 to see the iPad but guessing it wouldn't take much to change that.
Hopefully somehow the PhaseOne backs show up a little more on Apples radar (I believe aperture supports hasselblad raw) so they might put in some raw support. I can see the iPad being a pretty nice field backup/cataloging device integrating very well with full desktop apps in the future.
But even without that, it may be useful as a CF card backup device when in the field. 10 hour battery life and 1.5 pounds is certainly a sweet combination.