Unless you receive a message that states you could not access a file, you don't need to repair permissions. Regardless of what repairing permissions reports, there aren't any problems unless it states it could not repair permissions. Even a fresh permissions database doesn't know what the current permissions should be. It uses what was current at the time the system is installed, and it rarely gets updated.
As updates change things, the permissions database becomes more and more out of date.
Now, if you are having a problem with iTunes hanging up, then that is not normally caused by permission problems.
Do you have any plug-ins or extenstions for iTunes?
Does it occur in another account?
Does it occur in Safe Mode? http://support.apple.com/kb/HT1455