Twice I've tried updating from OSX 10.5 to 10.8 on my 1.8 GHz iMac, and both times it seemed to be stuck for awhile in the stage with, I think, a grey screen and the circular ring of bars rotating (not the spinning beachball of death)... for over 20 minutes. I couldn't start back up without software CD. I eventually had to reinstall 10.5 and, the first time, I had backup (Time Machine), but my iPhoto and iTunes libraries and QT movies were empty, gone. I just wanted to update to 10.8... Now I'm afraid to try. Help?