As some have said, I do hope that Apple pays some attention to their creative base. In the visual arts, Apple is a clear leader, and I think they should at least tip their hat to creatives with their production devices (as cool as it is with apps, the iPhone is more of a "receive/interact" device than a "produce" device).
I don't expect to have the tablet run full-on Photoshop like a champ, but if it runs it at all it can be used for small, on-the-go sketches, ideas, touch-ups, etc.
Photoshop's resource heaviness is somewhat tied to the size and complexity of the file being worked on. A hi-res file with 100 layers can bog down big machines, but adjusting levels on a web JPG doesn't really eat a ton of resources.
No matter what, I think Apple should do a one-two punch to Kindle and Wacom. Awesome capabilities to store and display formerly printed media (magazines, books, newspapers); as well as linking up with more powerful devices as a write-on-able Cintiq-like display extension - as some have already mentioned.
The entry-level Cintiq is $1000. Even if the Tablet doesn't have ALL the features of the Cintiq, if it comes in lower than $1000 and does a bunch of other stuff on top of that, then I can see this being a device that will do very, very well.