Since the PDC is over and the Beta has been released, I can finally tell you what I have been working on - Direct2D.
This is a native code graphics development platform for 2D graphics. There has been a lot already written about it to read.
We have white papers here:
And the PDC2008 video can be found here:
This has been a great product to work on and I am excited to see it revealed to you all. Feel free to give feedback to myself or the other D2D team members who have blogs (links on the left).