I've been having a lot of fun playing with the subset of functionality that is in the current release. If you're familiar with WPF already, you'll have no problems transferring those skills across. The feature set is relatively limited in the current CTP release, but you can already do some pretty fun things with it. The download is small (complete install with no other prerequisites in 2MB on Windows, 3MB on Macintosh), and we're working hard to keep the size as compact as possible.
Another comparison is of course between WPF and "WPF/E". WPF remains our flagship client platform API, enabling powerful Windows applications to be built with XAML, C# and the full underpinnings of the .NET Framework 3.0. On the other hand, "WPF/E" is aimed squarely at the web continuum, providing a great partner for technologies like ASP.NET AJAX. It's our hope and expectation that both technologies will have a long and illustrious future as solutions for different spaces.
I'll be posting quite a bit about "WPF/E" from now on, interspersed of course with continuing posts about WPF.
[As some of you may have noticed, I've been quiet for a few weeks. Microsoft is generous in offering four weeks' paternity leave for fathers, and since we welcomed our third child into the world at the end of October, I took advantage of the opportunity to take time out to recharge. It's good to be back!]