Amazon had a sweet deal on Sketchbook Pro (Mac/PC version) last week, and as part of the bargain I snagged a Wacom Bamboo stylus for iPad & iPhone. The rationale for this was to have a way to doodle ideas on my iPhone and send them straight to my home computer via DropBox for editing later. Now that I've been using it for a few days, I think this system will work out nicely.
Just as a clarification the Bamboo stylus isn't the same as the pen that comes with their Bamboo pen tablet. The styluses (styli?) for the pen tablets won't work on an iPad or device with a similar touchscreen. Instead of the plastic nibs used in Wacom's pen tablets, the Bamboo stylus has a rubbery nib that mimics whatever it is that's special about your fingertips. I don't know how it works, but the results kind of speak for themselves: [link]
It feels like drawing with a Sharpie marker, but it is possible to do really detailed work if you've got the patience and inclination. Carlo Ostrout of "Life After Death" [[link] and Elizabeth Fernandez of "The Code Crimson" [link] have been making their comics from start to finish using iPads for some time now. They may lack the processing power of a desktop machine, but you also can't sit in a recliner with a computer and Cintiq tablet very comfortably. I'll probably never draw a comic while sitting in a canoe in the middle of a lake, but in all honesty, the possibility is pretty enticing.