MS Research had a neat demo on this very topic some time ago.
Edit: never mind, it seems they use their own hardware. In that case, it would be interesting to know if iOS allows fast raw access to the external periphery.
It should be noted that unless Microsoft had a 1000Hz display running, there was something fishy going on with their 1ms update.
http://owenimholte.wordpress.com/2012/03/30/ipad-3-screen-re...
Paraphrased from our Kickstarter page: Thanks to those that have identified an issue with our drawing video clips, they were shot with a high fps camera and included in our video at HALF SPEED. In response, our video will be adjusted to demonstrate the drawing at normal speed. Additionally, we have identified areas to further optimize our algorithms for you to ensure that any latency is fully minimized. You can consider drawing speed to be equivalent experience to the iPad touch interface; if not better. Cheers, Rob (CEO) Collusion
By the way we are now 'de lurking' as we have finally got some sleep after the marathon lead-up to the kickstarter launch - 53 hours and no kip is not pleasant! Feel free to ask us questions directly. There is a LOT of work going into Collusion to address many of the existing fundamental issues of pen on tablet computing (many raised right here on hacker news inc latency, accuracy, palm rejection etc) we kindly ask you do this before reaching for the nearest pitchfork:) Talk to us.