If you have got a Nexus 7 (2012 and 2013 Wifi models) or a Nexus 10 you may want to start checking for the big update right about now, as the OTA to KitKat has been released into the wild according to the official Android Google+ account.
The 3G versions of the Nexus 7 and the Nexus 4 have still got to wait though.
To accept the OTA as-is, you’ll need to be running the latest stock build from Google, though an unlocked boot loader should pose no problem.
If you like me are a messer, (ie the user of custom ROM’s) and don’t want to go back to stock you’ve got a couple options. The easiest, and recommended, is to sit tight and wait for someone to convert things into a zip file that can be flashed with any recovery, which will follow shortly after the OTA gets into plenty of hands.
Or you could also quickly flash the last factory image, or you could just wait and see if Google releases a new 4.4 factory image.