The WPF Team at Microsoft has posted the 0.1 edition of the WPF Application Quality Guide. There's still a lot missing, but it does have good tips on how to set up your WPF application for automated testing.
Here's a list of tools they recommend for performance profiling:
Using Performance Profiling Tools for WPF.
Event Trace. Use this tool for analyzing events and generating event log files.
Perforator. Use this tool for analyzing rendering behavior.
ETW Trace Viewer. Use this tool to record, display, and browse Event Tracing for Windows (ETW) log files in a WPF user-interface format.
Visual Profiler. Use this tool for profiling the use of WPF services, such as layout and event handling, by elements in the visual tree.
Working Set Analyzer. Use this tool for analyzing the working set characteristics of your application.
I also feel the need to plug the best visualizer out there, Mole!