I love using the iPad with Sketchbook pro. Although there are some limitations. For example there is no presure sensitivity the way Sketchbook Pro works when using a Wacom Tablet.
Besides that its great for everything else.
Now I'm looking to purchase the Cintiq from Wacom to really have the total portable Sketchbook feel.

Until then I'll be posting some of my sketches from the iPad. Here is the screen saver  I created for my Ipad.