Just found out the hard way that the following things result in unintentional deauthorization (i.e. you will have to consume another 1 of 5 of your authorizations to reactivate) of your machine to play iTunes purchased protected AAC's: 1.) replacing the motherboard of your Macbook Pro (had mine changed twice because of faulty logic board) 2.) doing a complete restore of system and user files via Time Machine 3.) transferring all your files to a new machine (remember to deauthorize old machine before disposing / erasing files on it.) I've consumed 4 out of 5 of my authorizations unintentionally because of the above. Thought I'd share the experience so that others may avoid encountering the same problem. P.S. Read on the Apple support site that I need to wait out the year before resetting my authorized machine count. Any way of getting around this?