This whitepaper is now available here. It's very short :)
There probably aren't a lot of digitizer OEMs subscribed to this blog. However, for the rest of you (software developers), there is good info here. We outline what the digitizer is expected to pass through to you so that when you subscribe to the data stream, you'll know what the data is and what to do with it.
For instance, X and Y (coords), tip switch (tap) and in-range notifications are required. So at a minimum, you can expect any properly written Pen or Touch digitizer driver to report these. What can you do with such data? Well, for starters, now you can tell when the pen or finger is down and you can custom render ink. Groovy!
Another suggestion might be to implement hover (in-range, x, y) in a game.
One subtlety to note for Touch digitizers and in-range, there is no current way to determine that your finger is say 2mm above the surface, so we fake in-range by sending it along with tip switch (tap) and correspondingly send out-of-range when tip switch is off. For example, using this technique, users can still invoke the in-place TIP with Touch.
P.S. I'll be in Vegas for Mobile Connections Nov 6-9. Come on down to Sin City and meet with your favorite Tester (me!) and the famous Stefan Wick and Todd Landstad, both of whom will be presenting sessions. I'll have new hardware (at least, that's the plan) to show you running the latest Windows Vista builds. It's gonna be a blast!
update: fixed whitepaper URL