I use an HP tx2000 series notebook/tablet computer (tx2117CL) with a 12.1 inch screen. For me the convenience of being able to use its pressure sensitive Wacom "Penabled" screen to edit on the fly and on the road using PhotoShop was a great feature (I use Wacom Intuos graphic tablets when I work on desktops). I was a bit dissatisfied when I discovered I had to purchase a more comfortable pen than what came with the HP tablet, since my standard Wacom pen and Airbrush would not work with the Penabled HP.
Granted the screen is smallish, but I have not found that a problem since I can zoom in and out on the work area with no problem. Additionally, it's 250GB drive provides a great place to dump photos, something I rarely need to do now, though, since I use several 8gb Extreme III and 4 cards when traveling. But the computer is small and able to fit in my camera backpack.