Adobe held a keynote yesterday at Photoshop World 2011 to demo an upcoming Photoshop app for iPad that supports a variety of interesting features that aren't available in the currently available Photoshop Express app.
Check out this video from Photography Bay to see the Keynote:
There is no word on when the app will be released, but it is still in development, so it will probably be awhile. The iPad's hardware is definitely capable of tackling a higher workload, so it would only make sense to make it a portable art studio.