There is a new technology out and freely available from Microsoft and it's called Windows Presentation Foundation. For your average web developer (beyond the name being a bit of a mouthful) there is nothing of interest here, right?
Well... maybe not. More traditionally it has been a pretty safe bet for web developers to ignore the majority of noise coming out on the Windows Forms platform or any Windows desktop technology from Microsoft and the .Net community at large. However, I think WPF is different due to WPF/E. If you are a web developer today, get the book and prepare for the "E".
For more information you might want to start here.