In terms of the NUI research project Squidy at the Konstanz University the TUIO overlay SurfaceToTuio has been developed for Microsoft Surface. Download the SurfaceToTuio component from the sourceforge project site (or via direct download).
SurfaceToTuio is available as source code only (there is no executable). However, you can just upload the SurfaceToTuio folder to your Surface, doubleclick the Visual Studio project and compile it in the Surface’s Visual Studio right away.
Finally, a decent software interface for a decent hardware.
Update: The project of the Konstanz University has a bug, which has been resolved by Julian. Check out the stuff in his repository.
Update 2: Now, another TUIO overlay is available for the Surface (2).