Nice, thanks for the link!
Edit: That was a good read, and something I knew I needed to get in the habit of doing. But using the motor shield I wasn't sure if I needed to since the shield handles all that, or so it seems. I have an ext_power block on the shield that I hook 12V to and it gets it to the motors. Maybe not having that ground connected had something to do with my H-bridge burning up the other day.