Looks so far like the only update actually being seen "in the wild" is the one for the 2013 Wifi Nexus 7. I have a feeling it's still going to be several days for the 2012 Nexus 7, and if you have a Nexus 4 it's going to be several weeks (December'sh) before Google get's around to Kit Kat for it.
They have only posted a link for the 2013 N7 image so far. We can't use the manual method until there are update images for the 2012 N7. But for those who are really impatient the Paranoid Android team have released a 4.4 AOSP ROM for the Wifi 2012 N7.
I've side loaded and everything seems to be working fine. I installed the apks of GEL 3.1.8 and the launcher and it all works. Transparent top and bottom panels, Google now on right swipe and 'okay Google' from the home screen.
I side loaded about eight hours ago and haven't hit a single snag.