If you want to learn Avalon, the PDC Hands-On Labs are probably one of the best sources of material currently available.  They were just posted to the general public.  These labs really allow you to walk through a bunch of different Avalon features and learn how they work.  I have done two of them myself (Creating Rich 2D and 3D Content and Creating Custom Controls) and found both labs very valuable as far as learning the platform.  Highly recommended.