-- EDIT (Nov. 2014): The smoothing groups addon had some problems with most applications besides UDK, and I ended up removing it. I'll probably revisit the idea at some point. The FBX exporter is still being updated. --
I've spent the last couple of days working on this and I think it's mostly ready for testing. This version if from last night, I've actually added some more features and fixed some things since my initial upload, but here's an initial testing version:
-- link removed --
The other addon is an fbx exporter with UDK optimizations and support for smoothing groups created by the above plugin and custom vertex normals as described in my last post:
Github - Blender UDK FBX Exporter
Proper documentation and updates will be up soon.