Both the Wi-Fi versions of the Nexus 7 and the Nexus 10 have received some KitKat goodness officially, but the 3G Nexus 7 and the Nexus 4 are yet to see the OTA update made available. Nevertheless, the Android 4.4 KitKat factory images are now available on Google's Android Developer site so they can be installed lickety split. This also means the OTA versions will be appearing very soon too.
You can head over to the Android Developer site for all the factory image download links as well as to get more info and install instructions if you need them. The installation instructions are pretty simple if you've flashed ROMs on your device previously though: just download the factory image and execute the flash-all.bat file. The Nexus driver binaries are also available.
If any of the download links are broken that would most likely be because Google are working on them, so just check in again later. If you're comfortable installing factory images, please be our guest, but if not, then we would advise you to wait, as the OTA updates will be pushing out very soon and we cannot take any responsibility if you do bad things to your Nexus while trying something you're not familiar with.
We already know that CyanogenMod, Paranoid Android, AOKP and Omni ROM are all working on their versions of the KitKat code base. Their job just got significantly easier, meaning you'll be able to have Google's version of KitKat or a custom ROM tweak in the very near future. If you don't have a Nexus but still want a taste of KitKat, just check our article about the new Google Search and Google Experience Launcher combination, available for any device, or our KitKat custom ROMs, themes and launchers article.
Have you installed the factory image yet? What are your thoughts on KitKat?