This is one that I came across last week when talking to Jeremy Likness from Wintellect at MIX and lines up with some of the previous posts that I’ve written about touch based applications (the last of which is here and links back to previous entries).
The Wintellect guys have published their “LightTouch” library for Silverlight to CodePlex;
so if you’re looking at touch applications with Silverlight then this is one more string to add to your bow. I’ve not yet had a chance to download and experiment with the library but I imagine it’s going to be pretty useful 
Mike Taulty 