Up on the Expression blog, a fantastic tutorial that isn't in the docs yet has been posted.  I just walked through the entirely thing step-by-step and it is probably one of the best resources out there for unlocking the power of EID and WPF.  It explains how to templatize a check box, how to create states, how to create events on a timeline and how to wire up media.  Most importantly, every detail of the walkthrough is explained.  There were lots of little secrets for using EID that I didn't know, like using the Timeline Properties to do state changes or even the Fit to Screen feature in the Zoom drop down. Highly recommended.