As Google traditionally sucks in the execution of any sort of update, some territories will get it sooner, some weeks later, as we seen from the previous Nexus device update rollouts. We had friends who got 4.3 on Nexus devices months after the initial rollout. Both the 2012 and 2013 Nexus 7 will be getting the update starting today as well as the not so popular Nexus 10 that is about to get a replacement, hopefully with a much faster chip that can cope with its immense resolution.
We played with Kitkat for the last week or so on the Nexus 5 and we cannot point to any killer feature that will make it really special. Having an OS optimized for 512MB memory when modern phones including Nexus 5 have 2GB of RAM is not something that will get us too excited, but reducing the OS footprint could mean a lot for mid-range devices.
Higher numbers are always better, so when it becomes available you should definitely update, at least to know that you have the top one and that most phones will never get Android 4.4.
The official Google + official post is here. (Since it’s on Google+ most people probably missed it. Ed)