The good folks that created the WPF/E SDK and documentation have a blog and it is a great source of information and samples.  If you're going to be doing any WPF/E development in the coming months, this is a great blog to subscribe to.

Some highlights include:

• A great overview of the WPF/E browser plug-in and how the XAML DOM relates to the HTML DOM
• Information about updates to the WPF/E quickstarts.  The quickstarts are an excellent way to learn about vectors, text, animation, media and mouse input in WPF/E all with interleaved live samples.
• A walkthrough for creating reflection effects in WPF/E
• A Virtual Earth / WPF/E mash-up with sample code and a walkthrough for each part of the sample.

Here's a pic of the Virtual Earth mash-up (click to run the sample):