I've been a huge fan of incorporating WPF into form-based projects since reading Kean's article:
Hosting WPF content inside an AutoCAD palette.
As the article suggests, I've mainly focused on Hosting WPF User Control(s) inside an AutoCAD Tool Palette. Admittedly, I've been stumped with WPF Tree View's mainly due to availability of time to work out some kinks. I've also stumbled to wrap my brain around the model-view-viewmodel pattern, and style Inheritence, & Triggers.
I even started to experiment with Google Map's free Javascript API + WPF + AutoCAD Tool Palette... Again, it has promise, but I have no time to overcome my learning curve at the moment.
My most successful WPF project was a Browser App that had a build stored on the Network, which functioned as a 'reference utility' having tabs for different criteria, forms, links, etc. to consolidate many of the critical resources our teams would need to access for our projects. Very useful, easy to deploy, and maintain... And works with Visual Studio Express.
Expression Blend looks very interesting to me, but will sadly not be something I use, unless work decides to buy, since there's no 'Express' version. Very neat though; I'd be interested in others' opinions as well.