One of the things I don't like about QAvimator is that it doesn't let me hit a button to flip or mirror an animation.
The .bvh file format that SL uses for animations isn't particularly complicated. To flip an animation is tedious but not difficult. The bottom half of a .bvh file has a line for each frame of your animation. You flip the negative sign on the Y rotation values for the center-line joints, then for the arms and legs you copy the values of the other side and flip the negative sign on the Y and Z rotation values. Not too frustrating on a pose, but on a moving animation? Ugh.
Fortunately Tali Rosca has made this a lot easier. Mirroring an animation? Try this!