Quicknote: If you are a wpf custom control writer(1), check out the sources for the Silverlight 2.0b1 controls released with mix08 keynote: Silverlight 2.0b1 controls. It is actually a whole vs2008 solution, so you can even “learn” how to create tests against custom controls.
BTW: The new -and right now “Silverlight only”- DataGrid is also included.
- tobias
(1) custom control != user control 