I posted this on the CGTalk forums, and although there might be limited interest in this topic on THIS forum, I thought I'd post it anyway.
And I'm trying to figure out if it's possible. I'm already aware that the iPad comes with no stylus and no pressure sensitivity... bear with me, I'll explain.
Jaadu VNC is an iPhone application that allows you to remotely view and control your Mac or PC with your iPhone. Several members of Apple forums have been in contact with Jugaari, the creator of Jaadu VNC, who have said that an iPad version is in the works. If that's true, that means that your Mac/PC - including ALL its applications (Photoshop, Painter) will be accessible from practically anywhere via your iPad. Theoretically, you should be able to use Jaadu VNC to make your iPad into a Cintiq-like device, being able to draw directly on the screen of the iPad using programs such as Photoshop and Painter. I've seen this confirmed in other forums by Jaadu VNC users for iPhone. The small screen of the iPhone was limiting, and there was talk of some lag, but they were able to do it.
The problem with the Jaadu VNC solution is that the iPad still has no stylus, and still no pressure sensitivity. In walks Ten One Design. This company has created the Pogo Sketch, a slim tube with a soft tip that acts as a stylus for capacitative touchscreens like the ones on Macbook touchpads, the iPhone/iPod Touch, and the iPad. I own one, and I find that it's a very functional device for the most part. As for pressure sensitivity, Ten One Design has also created an application called Inklet, which uses the Pogo Sketch to turn your Macbook trackpad into a PRESSURE SENSITIVE tablet. Now, I can't really recommend Inklet as a replacement for an Intuos or even a Bamboo, because it doesn't have a "hover" function that allows you to take the Pogo off the trackpad. You basically lose the cursor if you lift your hand, and needless to say it's not easy for anyone to draw if you can't lift pen from paper. BUT, that problem would be resolved for the iPad, since you don't need to drag a mouse to get the cursor from place to place. And I can vouch for the claim that Inklet registers pressure sensitivity; I don't know how many levels, but it's certainly there.
Imagine if Jaadu VNC was able to work with Inklet to make the iPad into a pressure sensitive tablet on which you could use full versions of Photoshop, Painter, any program you like! In my opinion it would be a real Cintiq competitor, especially for those new to digital art (yes, like me, I've been a traditional media artist and have long wanted to make a switch to digital, but found the hardware prices too steep). Now, I'm not harboring illusions that this would make the iPad into a Cintiq EQUAL... after all, there are no express keys, no pen switches, no pen eraser, and I can only imagine that the soft, nubby Pogo Sketch would be less accurate than a Wacom pen, with fewer levels of pressure sensitivity. Also, you would only be able to mirror your Mac/PC screen, you would not be able to use dual screen. BUT, on the pro side: 1) It would be truly portable, unlike the Cintiq 12wx with all its cables. 2) You would not need to have a PC right beside you, unlike ANY Wacom tablet for which the desktop/laptop computer would need to be present also. 3) It would be cheaper. The iPad starts at $500. Inklet costs $25, the Pogo Sketch costs $15. Jaadu VNC for iPhone costs $25, the iPad version will probably cost more. Compare that to the cheapest Cintiq model for $1k.
Of course I should mention that this solution would only work if you also happen to have a Macbook with a capacitative trackpad. Still, this is interesting, no? Tell me what you think!