We released the Encoder SDK today. You can download it from the following location.
Microsoft® Expression® Encoder 2 SDK
Once installed, it will create a Start Menu shortcut under Microsoft Expression which opens an explorer window to the SDK directory.
The SDK installs a couple of XML files which enable intellisense comments within Visual Studio.
There is a Docs folder which contains the help file along with a PNG of the object hierarchy which can be printed if desired.
You'll also see a Samples directory which contain the actual samples. If you're running Vista and you want to build the samples directly from this location, remember that you'll probably need to run Visual Studio elevated.
The help file contains an introduction, details on the samples, the API reference and a few other bits and pieces.
We hope you find this useful, and please send us your feedback.