I have twice now had all my printers disappear from my System Preferences, even though they show in the Printers folder in the User Libary (~/Library/Printers).
Both times, the printers were working fine after the upgrade to Mavericks, but when I shut down at night and came in the next day and rebooted, they were gone.
Both times, I have only found one solution to get them back again, so I am posting it here, but I am hoping someone can aswer why they are disappearing in the first place.
Solutions that DID NOT work:
Rebuilding preferences, any of several methods of doing so.
Running Disk Utility, any of several methods of doing so.
Simply copying a new copy of the printers into the folder from a backup.
Solution that DID work:
1. Open the Printers Folder in your home Library (~/Library/Printers)
2. Enter Time Machine
3. Go back to a date before the printers disappeared
4. Restore all the printers you find in the folder
5. When it asks you if you want to overwrite the existing printers, say Yes.
Viola! Go back to System Preferences and you will now see your printers back there again. You don't even have to reboot.
Retrieving data ...