right.. leaving orientation checked allows you still rotate as stock (trackball down, and trackball to the right).. selecting the second option, 180 degree rotation, allows you to position the trackball at the top, bottom, left, or right, depending on on convenience. afaik, the ipad is the only other touch os that offers this.

the reason this feature works for me is because i like to lay in bed and hold the phone in my left hand w/ the trackball facing left.. just more convenient, and thanks to cm, i can now do this. :)