The upcoming version of the decompiler SDK adds some nice features.
First, we created a reference manual. It is in doxygen format: cross references make it really easy to browse. Second, the SDK is compatible with both IDA v5.1 and v5.2. Third, we added functions to retrieve and modify all user-defined attributes like variable names, types, and comments. Fourth, we added more sample plugins. And fifth, our forum is open. All your decompiler and SDK related questions can be asked there.
Since the “show, don’t tell” rule applies to everyone, here’s a short video demonstrating one of the new sample plugins (it displays the decompiler output as a graph):