You didn't mention how long deploys take. 2GiB x 80 servers = 160GiB; assuming a 1Gb/s interface on the repository, it'll take a minimum of 22 minutes for all the servers to get their new bits.

The nice part about Docker is the images are composed of layers, so you only have to re-download a layer when it changes. In practice, we pull all of our base layers when we bake our AMIs, so spinning up a new instance is pretty quick and each new deploy only has to update the top layer that contains our code.

Honestly, the only issue when it comes to image size is the initial developer pull either when they onboard to a team or when they bork their boot2docker install (which, disturbingly, happens way too often).

Many applications are very large (consider a Rails app with all of its prerequisite Gems). Granted, this isn't Docker's problem, but it presents practical distribution bandwidth constraints that Docker doesn't currently solve well.

Not every server runs the same applications, we mostly do deploys on 5-6 servers at a time, it takes around 3 minutes to deploy our biggest apps, most of them deploy in under 30 seconds.

600 MiB? That more than a complete OS install. Isn't an image supposed to be one application only? Do you store data in them, or why are they so big?