I’m happy that you like the app. GfxTablet pressure sensitivity is handled by the MotionEvent API automatically. I think if there’s no hardware support for pressure, the API tries to emulate it – so the pressure info should be available to all apps, no only GfxTablet.
I’ve just finished my first foray into Debian packaging, and hence a PPA is now available at http://launchpad.net/akdor1154/gfxtablet. You can add it to your Ubuntu system with
sudo apt-add-repository ppa:akdor1154/gfxtablet
sudo apt-get update
sudo apt-get install networktablet
It’s identical to what is in rfc2822’s master repository. Currently it needs to be run as root (or else grant your user access to /dev/uinput) but I intend on fixing this.