With the public availability of VS2010 beta 2, the MSDN documentation has also been updated.
Two pages that any touch developers should read are:
What's New in WPF 4: Touch and Manipulation
Walkthrough: Creating Your First Touch Application (Basic scatterview-like pan/rotate/stretch on a rectangle.)
It's pretty easy to get started. I actually wrote a program similar to the walkthrough (before finding the documentation) in about 30 minutes.