built in to Ubuntu, works pretty well.
Maintains "focus" better than XVkbd
(may need to be turned on in System>Preferences>Main Menu>)
haven't yet figured out how to auto-tile windows when on-screen kbd is called up..., or even do it manually
OR how to use on-screen kbd when prompted for Admin password...
Wacom tablets in Ubuntu guide/howto
... which links to
Linux on the Lenovo ThinkPad X60 Tablet
Last updated: 2008.09.26
Created to be X60-specific, but still has tons of good tips about screen rotation....
So, it looks like it works, but could be improved. For one thing, I would like the recognition to just take place over any window. Or at least have window docking make other windows get out of the way. And there are obvious recognition issues/problems with expected things like t and +, c and <, etc.
I guess what I really want is something like No-Cell Writer