The Nexus 5 is the only device that has shipped with Kit Kat to date. Some other devices that should have seen the update quickly have not seen it as quickly as expected. If you own a Nexus 5 and love to flash roms there is a 4.4 based rom for your device. Omni Rom is a community based Rom that was announced at the big android bbq with much fan fare. This Rom is still a work in progress, but you can download the nightly builds for flashing now.
There are no known bugs in this rom other than a lack of data for the sprint variant. There is a patch for that so even Sprint users can join in on the fun. This is one of the first ever custom builds of 4.4 for the Nexus 5. There aren't many custom features in this rom yet, but they are surely on the way. Check out the source link below for the download.