Writing exporters is boring. It mostly involves navigating huge unwieldy and poorly documented APIs.
I'd like to spend as little of my time as possible writing exporters, and I'm guessing most other developers feel the same. So, in that spirit I'm sharing the code of the simple Motion Builder exporter I just wrote:
BitSquid Python Motion Builder Exporter
Feel free to cannibalize the code for your own exporter. Hopefully you can save a little time and spend it doing something more interesting than writing exporters.