If you're interested in the new rendering engine used by Longhorn, you should read Chris Anderson's latest article on Avalon, “The Blinking Lights Division”. It greatly assisted my understanding of the subject. It seems that the focus is always on XAML markup, and you probably know that it's possible to add shapes (elements, visuals) with plain old code, but did you know that Avalon also has an equivalent to the GDI device context called the DrawingContext, with methods like DrawRectangle()? Great stuff; it's all starting to make sense...