I've heard a few folks recommend starting using http://codelaboratories.com/nui.
Their platform includes a "WPF/C# (.NET 3.5) Visual Studio 2010 Sample Application," and there's plenty of discussion on sites like http://nuigroup.com/forums/viewthread/11249/
about it. - Also, see https://stackoverflow.com/questions/tagged/kinect
for more information.
Whatever you write, keep in mind that the official SDK is on its way - I'm guessing a CTP will be ready soon after MIX11?
You're in pioneer territory, so expect to run into a few issues along the road, but have fun!