Flotzam mashing up Twitter, Facebook and Flickr in WPF
Take a spoonful of Twitter, add some Flickr and a dash of Facebook, optionally flavoring to you own taste with custom RSS support and you have an application that doubles as a screensaver flowing data on and off your screen. Better yet, remix the app by grabbing the source code and customize the whole experience.
Kartsen and Tim talk about their development experience especially focusing on the flow of between designer and developer. Tim designed the elements within Blend, handed them off to Karsten who would then write the C# code which reach out and grab the disparate data and display it leveraging Databinding.
Karsten blogged about his experience here, but I would expect to see more from him about the Designer/Developer workflow in the future.