I have been evaluating WPF/E for add-ins to my company's products. One screen we have been thinking about for a while is a lead pipeline that shows lead stages in a graphical way. Our products leverage IE for the presentation layer and it is tough to do a compelling pipeline with just DHTML.
WPF/E brings a lot to the table. First of all it is very easy to incorporate into our screens, I simply insert the control code and link in the aghost.js file. It also enables us to easily separate the markup from the script. The HTML file orchestrates the screen while the script and XAML reside in separate files. I also like the division of labor. As shown in these screenshots I've coded the pipeline screen as a segmented pipe along the top of the screen. 
As the developer I just created simple XAML objects that represented the different elements of the pipeline, nothing too fancy. I then hook up my script to control click-thrus and mouse-overs (the second screen shows how the mouse-over affects the pipeline). In production I would then had the XAML source over to a designer and they would take my rudimentary design and create something beautiful from it. They'd send me the updated XAML file and I just insert back into the development tree and everything should still work with changes. In this case I was the designer too, but you should start to see how this should make development easier.
Another thing that I experimented with was trying to use the same XAML objects and provide an entirely different look and feel for the screen. The final screen shot shows how that turned out. This pipeline demo is very simple, but it starts to paint a picture of how WPF and WPF/E can be used in software. I can imagine that things are not quite as simple when more complex functionality is needed. When trying to change the pipeline into a vertical funnel, I did have to adjust some of my code to make it work.
I did try to use Microsoft's new Expression Design application to create the XAML I used in this demo. I designed the circular pipeline segments and exported them as WPF/E XAML code. That sort of worked, but It generated everything as complex paths and was hard to modify by hand. By the time I had finished the demo, I ended up starting from scratch with the XAML objects. Still, the tools are great and they look very promising.