The last I knew the keys weren't used anymore. Early into EQ Verant had planned to have certain doors in Unrest be locked. In order to unlock a door you needed to kill a certain creature, loot that particular key, and then you could gain access. The doors are no longer locked but the keys still drop. Perhaps removing the keys was more difficult than having the PC's destroy them. I have been in Unrest from 14th to 31st levels almost exclusively and have not found a locked door yet.
Zahmlikker Cheekeemunkee
31st season Dwarf Paladin