I tried this with my iPad (the new one) over Easter, and it generally worked quite well. The editing was reasonably fast, fun, and easy. I was editing "snapshots", rather than photos that were incredibly important, so a tablet was just fine. Where this scenario failed though was exporting the images from iPhoto. That program is incredibly obtuse! For some reason, I could only get it to export each image to the camera roll one at a time, rather than all at once! I had 30 images, so that meant performing the export function 30 times in a row!
Oh, and the Facebook upload tool kept crashing. This app needs a lot of work.
All that said, I do see significant potential here for the future.
PS: This entire post was written using the voice dictation feature on the new iPad, and I'm surprised how well it works in a quiet room! Eat Martha's socks.