Ten One Design has made a reputation for themselves by providing tools and technology to turn touch-sensitive surfaces into drawing tablet style interfaces. They sell a Pogo Stylus that works along with the capacitive touchscreen of the iPhone to make it an even better tool for artists. And in the video above, they're showing off a tech demo that seems to have a modified version of the Pogo Stylus that makes pressure-sensitive drawing possible on Apple's iPad.
Unfortunately, Ten One doesn't have software to sell yet; the tech above uses a private API call, which means it couldn't be approved on the App Store. As far as I can guess, they're somehow passing pressure information back through the stylus to the iPad, since the iPad's screen itself isn't pressure sensitive at all.
No matter how they're doing it, though, it's cool. I don't think this is exactly what Jobs expects the iPad to be used for, so it's not likely that we'll see official pressure sensitivity on an iOS device very soon. But it's cool to see a video like this that shows off the potential.
Update: As a few of our observant commenters noted, there's no Bluetooth call here -- the private API call is just tracking the size of the touch on the iPad's screen -- bigger touch means more pressure and a wider stroke. That does seem like something Apple could eventually implement, so hopefully they will make that official in the future.