1. I think putting a flip(horizontally) button would would better than the mirror button. If you have deformations, mirror never works, but copy will copy anything, so if there was a flip button, I'd be happy.

2.The face bone size doesn't get saved. It should. could you tell me where in the registry, I could make that happen.

3.Onion skin. You should be able to change transparency of the one your on and the one your referencing seperatly to the users preference