I wrote a fair amount about graphical composition in Avalon here:

http://www.ondotnet.com/pub/a/dotnet/2004/03/08/winfs_detail_3.html

That one's got a fair amount of discussion in the comments between me and some Mac people.  It gets quite heated, but you might find it interesting if you're looking for comparisons.

And also, I wrote some stuff on the graphics system here:

http://msdn.microsoft.com/library/en-us/dnlong/html/avalongraphics.asp