Like others have mentioned, tablet PCs have been out for a long time. But they suck shit because full OSes are not optimally built for such devices, whereas Android and iOS are.
Give it some time and you'll see Photoshop comparable - if not Photoshop itself - available for tablets. The market is still young, and development is gaining momentum. If you can't wait, there are some very competent paint apps available on iTunes already. Not sure about Android market yet, though.