Some folks have asked where the official documentation is for WindowsCodecs. It's there in MSDN, but it's not with the rest of the WinFx Documentation (mainly because the WIC APIs are unmanaged). The official MSDN Documentation for WIC is here:

Further, as has been mentioned previously at the PDC and other forums, the BitmapEffects infrastructure is also extensible. We have a cool sample coming soon... but until then the official MSDN Documentation for writing your own BitmapEffect is here: