[Dkt01]

Ether-
We actually ended up doing what we called a "Pac-Man drive". Our system compared the values for the x and y axes and only used the greater of the two. For example if the left joystick was in a position where x=.8 and y=.2, the robot would move right at 80% speed.
You are correct in saying the robot would only go forward/backward or strafe, but no combination. This solved our unwanted rotation problem.
We also used a custom dead band because the XBox controllers never went back to the exact same spot, but other than that we never had any issues. Unfortunately the directional arrows on the left never gave us usable input values, otherwise we may have used them for something.