I hear you. I like the idea of "deploying" a pre-built image. Capistrano "just-in-time" deployments (particularly deployment time "bundle") seem a little non-deterministic. Docker is certainly non-trivial though, but I think (I hope), it's a net win. Time will show.

In my mind, it certainly parallels the binary package (debian) vs build-on-demand package (arch? OS X brew) approach. Both seem to work, but I certainly prefer the debs.