We have two brand new 21.5 base model iMacs. This morning we ran software update and installed the Thunderbolt 1.2 update. Both iMacs have Apple Wired USB Keyboards. Both keyboards are now completely non functional. SMC reset and PRAM reset doesn't fix it. Plugging the keyboards into other macs (with or without the 1.2 update) and they are still non functional. Spent over an hour with Apple Support and they are stumped as well and are passing this up the chain to engineering. The USB ports are fine. If you plug a generic PC usb keyboard into the iMacs, they work.