This is an optimized version of a previous script. The main difference is this one runs about a hundred times faster.
Unlike other mirror scripts, this one doesn’t care for the location of vertices, but actually looks for the interconnections of all vertices and faces.
Make sure your mesh has at least one key. Make sure the key you want to mirror is active and selected.
You have to align the vertices which belong to the middle seam with the X axis of your mesh (x=0 plane).
If everything is OK, you will be prompted to mirror to X positive or negative or to flip. If something is wrong, the script tries to signal where the error is.
A new key will be created. Because of a bug in Blender 2.4, the Ipo window and the Shapes panel don’t get updated after creating a new shape key with Python. Be careful, because sometimes Blender can crash.
I have been told this feature is already in the Orange branch, and eventually will make it in the official release. For now, we mortals can use this script.