This is an intriguing bit of software for Macbook's. It turns the trackpad into a tablet.
Inklet by Ten One Design
YouTube- Inklet Demo with Photoshop
I have never seen anything like it before and I wonder if there's also a Windows one by someone else, trackpads being all pressure sensitive. Though considering the size of most windows laptop trackpads it wouldn't be very usable.
I downloaded the demo and whilst it isn't that great with a finger as the stylus, I suspect it would be very good with a pen. I've tried my Wacom Intuos pen and it won't work so there's something special about the Pogo pen they also sell (must have a built in finger).
Would be good to have a little tablet on the MBP when travelling, so I might invest in this pen and software I'm thinking as it's not very expensive.