Rebooted; it works, sorta. One of the two pads is ~75% on-screen with the navigator on the left (or right); with the navigator on the top (or bottom), or in full-screen, 1 pad is on, and the other is about 35% on.

So it's usable, if you have a sane configuration and don't mind using one pad. I'd rather use both; but the functionality's there.

Unfortunately, I think it's too wide to ever fit both pads on with the navigator on the side. I'll post a couple screenies momentarily to demonstrate what I'm talking about.

(Dug up an old post of mine; perhaps I'm one of few who really wanted this...)

The most promising one looks like xscribble, that's graffiti-like stuff. It's also got a website last updated in 2003, and a version number >1 (1.3), so mixed news.

Also matchbox-stroke, xstroke (GPL), but the place it's supposed to live is down, the other xstroke (non-commercial license), and perhaps some others.

The Agenda VR3 had graffiti-like stuff, but I'm not sure how easy it is to extract it, or even where the source is to be found. (I used to lust after these, way back in the day...) Here's some info, though.
http://agendawiki.com/cgi-bin/aw.pl?HWRProjectPage
http://agendawiki.com/cgi-bin/aw.pl?RecdInvestigation
http://agendawiki.com/cgi-bin/aw.pl?Andys/UsingAgenda