Just read an excellent article about the new Windows Presentation Layer in MSDN Magazine(read an introduction here) which was very interesting. I've seen some demonstrations of the tecnology earlier on, and read some blog postings about it without really becoming a believer. I even saw a demonstration of Sparkle on channel9 which impressed me a lot, especially in the UI departement.
The thing that got me started downloading the SDKs and development tools was the way you can focus on what the application should do and not how it should do it. While reading the article I could see that a lot of the problems and challenges I've met as a Windows developer in the past 15 years would easily be solved using WPF and the declarative model its using.
The ability to bind controls to objects, declare templates and styles coupled with the dynamic scaling of the user interfaces should be able to solve almost any problem I've been exposed to UI wise.
The only challenge left is to create a near-perfect model of the domain we're solving problems for :-)