Chandima Cumaranatunge, co-author of the O'Reilly Adobe Dev Library book ActionScript 3.0 Design Patterns (
http://www.amazon.com/dp/0596528469/), has posted a demo and very articulate introduction to PureMVC in his recent article at:
http://www.as3dp.com/2007/12/27/minimalist-mvc-example-using-the-puremvc-framework/-=Cliff>