Andreas points to this interesting article of unusual use of iPad for photographers (though it could work for many others too).
Just one word from Ctein made me take notice: "yet". As in "there's no pressure sensitive pen for the iPad. Yet."
I had sort of been thinking that pressure sensitivity was build into the Wacom Cintiq itself, which is silly now I think about it: it has to be in the pen! In connection with software in the tablet, of course. The pad has bluetooth, I don't see any barrier for anybody making a pressure-sensitive pen for the iPad for making professional art. And then we will for the first time have a quality, serious alternative for artist to to the exclusive Wacom machine. Not to mention the iPad is portable, much cheaper, self-powered, wireless, and can do a ton of other things the Cintiq can't. Very interesting.