Flipowitter: alpha stages of a simple Windows Pownce-Twitter+ client. Current version simply posts a note to either Pownce or Twitter, or both in sync. (Will post to whichever service has credentials provided.)
Plan to add Flickr, Picasa, Facebook, LinkedIn? tie-ins.
No, I'm not publishing source just yet, I have a bit more work to do, but the assemblies are service-oriented, and can be used to authenticate to Pownce or post a note from any .NET client.
As far as I'm currently aware, this is the first public .NET client for Pownce ...