If someone does manage to make an iPad-like device with pressure sensitivity, a decent stylus, and a good painting app, I'd buy it instantly, of course.
Personally, I use a laptop as my desktop, and I can run everything I need just fine (Photoshop, Flash, the works.) Depends on the laptop, I think. For me it's more convenient in my small apartment, plus I can take it with me when I go places, and I don't need to pay for and maintain two whole computer setups.
Not only that, I've heard Google/Android is working on their version, too... Personally I'm waiting to see where this all goes. The iPad as it is now is kind of like an expensive toy as far as I'm concerned - neat, but not really worth the money to me. But one way or the other, it's bound to turn into something much cooler (and probably cheaper) in future versions. (Whether the coolest versions come from Apple or someone else remains to be seen.)Oh, and to backup my view on the iPad of being the start to bigger things, here's a small article in which Bill Gates states that Microsoft is currently looking at a bunch of tablet projects. I somehow doubt Bill wants to take on Wacom.