Nick has written an in-depth post on a method to write reusable widgets in WPF/E. This is really a mini-framework to help address some limitations of the February CTP of WPF/E. Nick's approach is XAML focused, in contrast to the code based setCallback method of attaching object based event handlers to WPF/E elements that Peter created and that most of our samples use (including WPF/E Pad and Tile Text). The article includes sample code as well as a description of each part of the framework.
While Nick's code provides some very creative solutions to limitations of the February CTP, I'm anxious for our team to address limitations like name scoping, instance based event handlers and expandos in a future CTP.