Thank you, Tacit, for that clear post. Eased my mind. Now I just need to decide if I want to use it. I guess I'd better hurry up and order my external drive because I should probably backup Lion into Time Machine before I do this, right. I am assuming I would have an unadulterated Lion that way should I decide to go back.
Rita
I'd actually suggest that rather than using Time Machine, you download the free program Carbon Copy Cloner. It will make an exact copy of your hard drive onto the external, so if you decide you don't like Mountain Lion, you can boot from the external and be instantly back in Lion without faffing about with Time Machine.
