I've used the Tiny Core Linux on Sony Tablet P. It is pretty cool to be able to use Linux on top of Android (although Android itself is based on Linux).
I used Pentium 3 emulation with 128MB of RAM. I used Hacker's Keyboard as the keyboard, and the keyboard is much smoother than the stock Sony keyboard. It is nice to have up, down, left and right keys as well.
This Tiny Core Linux will come in handy when I want to scribble notes and tinkering.