On March 30th the London .NET User Groups presentation we be Ian Griffiths talking about Avalon. The session description is yet to be confirmed, but will include the whys of Avalon and the how tos of XAML.
With the announcement that Avalon and Indigo will be backported to XP/2003 it is becoming even more relevant to begin the process of understanding this technology now, so you are ready when it arrives.
Venue is Microsft House. Feel free to start signing up.