I have been playing with WPF for quite some while now and have been involved with several applications being developed using WPF.
Based on that I want to share my thoughts on when to use WPF. I searched a little bit for what the experts have said on this topic and ran found blog entries by Pablo Fernicola and Tim Sneath on this topic. Though these provide some good insight, I'm personally not convinced about the clarity of the message.
There are several marquee applications like iBloks, Rezn8, Northface that illustrate the richness of the platform, but for me there is no better application to drive home the point than the Healthcare demo especially for the enterprise environment where the key is enhancing productivity.
WPF should not be used just to be able to have stylish looking UI with zoomable multi-state 3D buttons (whatever that means). For me WPF solves one of the biggest problems with user experience - data visualization. How can an application present complex data to the user that provides a highly flexible and customizable way for the user to find the right item doing very little work (or clicks) or minimal guidance on navigation.
There are some great applications that are in the works that some of our partners are building and I plan to provide some examples of some good user experiences that WPF can enable.