The most notable difference at the moment will be:
- The computational power difference between a PC & a tablet - tablets give you the computation power of a PC that is 6-8 years older, so even if you get the workflow on par with the PC, the speed will definitely be a lot slower. If you are working with the RAW format, then just exporting them after processing will take a lot longer than on a PC - even the fastest hexa-core desktop CPU today equipped with an SSD takes 11 seconds in the Photoshop CS4 retouch benchmark.
Quoting from an article on Blackberry vs iPhone (written in 2008, well before the iPad, but quite relevant to the PC vs tablet computation power discussion) regarding the rate of progress in computation power:
...in just nine years, the specs that then described Apple’s top-of-the-line desktop computer now describe their phone.
The storage space available - tablets top out at 64 GB, so you are going to be severely limited even if you just go the JPG route
Connectivity options to transfer images from the camera to the tablet - more of a lack of or non adherence to standards than anything else though
Interface - Point & click may be a better accurate paradigm when trying to edit photos precisely. However, you can get over some of the limitations using a keyboard dock and\or stylus combo.
At present, a MacBook Air or Ultrabook is the most portable replacement for a full size laptop, and even a desktop that doesn't involve as many trade-offs as a tablet.
Update (post iPhoto for iOS): Touch devices do open up new forms of image editing, particularly from the ease of use point of view (once you learn the interface). There is a precision vs simplicity trade-off, but this should be good enough for all but rigorous editing. Do check out Andy Ihnatko's experience where he has shared some of the killer features. There are also quite a few iPhoto clones coming out now.