A tool called InvokeStress has just been posted up in the Developer Tools area on the wpf.netfx3.com site by a tester from the WPF team.  This tool is amazing: it uses UIAutomation to randomly click any UIElement every three seconds.  It is a great way to hammer your application to discover bugs and issues.  And, with the source posted, you can tweak it by using the UISpy tool from the Windows SDK to create your own stress runs that follow particular paths based on the UIAutomation IDs.  Highly recommended.