Many folks are irritated by the authorization limit in the digital-rights management system that Apple uses to handle songs purchased from the iTunes Music Store. You can authorize up to five machines to play songs purchased with your account at any given time, and you can de-authorize and re-authorize at will.
However, if a machine dies, is stolen, or you're visiting someone and authorize their system, de-authorizing becomes difficult or impossible. Apple will let you de-authorize all machines at once, but allows you to do so only once per year, making it only a partial solution.
<http://www.apple.com/support/itunes/musicstore/ authorization/>
I had a thought today I haven't seen written about anywhere - how about time-bounded authorizations? Let me authorize a machine for a day, a week, a month, or a year, and to re-authorize, I would have to enter the account password again at the end of that period.
My approach would still keep Apple's five machine limit, but entirely eliminate the problem needing only temporary authorization. If I visit someone and want to play my music through another Mac, I would be able to authorize it for a day, until a certain end date, or another period of time.
Similarly, Apple should offer free de-authorization for any Apple-authorized service repair. If your drive dies or they swap the machine out for some reason, one of the checklist items should be to de-authorize that machine automatically.