I work for facebook and I worked on the deployment of these large hiphop binaries of our code base. We considered multiple options - binary diffs, multicast, etc. The problem with multicast is that it's hard to configure and maintain in our complex cross region datacenter setup that has to travel through other peering networks.
We ended up with a torrent deployment system that scales beautifully.
We ended up doing exactly the same, I wrote a tracker for the bittorrent deploy system that is aware of our network topology and able to transport these 500Mb binaries to our frontend pool in < 3mins (300+ servers)
I remember reading that on paper it seems it should be faster but in reality not so much.
Ah okay, hiphop IS faster:
http://php.webtutor.pl/en/2011/05/17/drupal-hiphop-for-php-v...
http://huichen.org/en/2010/06/wordpress-3-benchmark/ Maybe multicast could be used on the intranet for distribution - but 500mb monolithic binaries sounds kinda insane.