Recently, after restoring backup from my Time Capsule, I ran into a problem where I’d have to reauthorize my Audible audio books every damn time I opened iTunes. Suspecting the usual culprit of problems on a Mac, messed up permissions (especially given the recent restore), I poked around and found the problem child. If you are having similar problems, I hope this might save you some time.
In Terminal, from an account with administrator priviledges, type the following:
sudo rm /Library/Preferences/com.audible.data.plist
It will ask you for an administrator password. Type it.
Now, after restarting iTunes, you should only have to reenter your Audible password one last time. Note that you have to be running from an administrator-level account for this to work. (Go to Users in System Preferences to enable your account as an Administrator, if need be. You can always switch it back to Standard once you’re done with the fix.)