MetaMorph is a Unity3d and Blender3d toolkit that allows mesh animation in Unity games using Blender shapekeys. It includes an export script for Blender that converts shapekeys into Diff maps and saves the animation data as text files. The MetaMorph script for Unity can read the Diffmaps and animation data in order to play back the morph animations in real time.
Demo is here: MetaMorph Demo
You can get the files here: Google Drive link
As of now, the most recent version is for Blender 2.58.
This thread at the Unity forums has more information: http://forum.unity3d.com/threads/175367-Blender-MetaMorph-Unity-and-Shape-Keys-revisited
I'll be trying to update this as I get personal time, but wanted it all in the same place for now.