I responded to detbear in an email, but for anyone else wondering...
If you have a symmetrical mesh and symmetrical bones, and you have made a smartskin for the bone "right something" you can go back to the model window, and choose "Mirror All Smartskins" and A:M will create a similar smartskin for the bone "left something".
You could also have started on the left side.
If "right something" and "left something" both have smartskins, A:M will use the most recently modified one as the source to mirror to the other side.
And, of course, you will remember to resave your model with a new version number after you do this maneuver.