Pretty much all of the developers have got the message now, Microsoft are doing somthing new in the vector graphics arena and they are sticking to their word about putting XML at the heart of everything.
With the Silverlight installed on a PC, a browser will render XMAL (XML) as cool animated screen elements.
While understaning that last sentence fully relies on your skillset, the toolsets are based on popular designs and easy for most to get started with.
The documentation has been a bit scattered but now as 2009 ends we can say that the online results content is fairly when you google a term, more importantly the community itself is up to speed on anumber of good quality resources, i.e. the whole thing is more mature.
Here's a few links which are useful for those thirsty for good tutorials
SDK based examples, good for those using Visual Studio 2008 sp1
Examples including Blend 2 and Visual Studio together