First, I have a clone and two separate Time Machine drives, so I'm covered if something were to go horribly wrong. My question is, in a successful reinstallation of Mountain Lion from the recovery partition, what exactly gets lost in the way of settings and preferences? I just want to know how much time I need to set aside to restore everything to the way it was, which will influence when I will do it. The reason for the reinstallation is a major problem with the Apple Mail app. It takes an age when clicking from one account inbox to another (sometimes several minutes).