Well your build system should all be in version control, so that a red herring. The issue with a developer building something and then throwing it over the wal

Well your build system should all be in version control, so that a red herring. The issue with a developer building something and then throwing it over the wall to ops is one possible workflow, but I think it's a stretch to say that's what Docker "encourages". It only encourages that if you have inexperienced people doing your build system. Docker actually dovetails nicely with DevOps movement to break down those kind of throw-it-over-the-wall silos, and if you have someone experienced and skilled in charge of your build, this poor workflow won't happen. So what do you gain? Well, you gain lightning fast, reproducible server deployments. You gain production / dev parity. You gain the ability to develop multi-node distributed systems locally without crippling performance overhead. Obviously this all comes at a significant complexity which may exceed your gains (hence why I say the jury is still out), but the problems it solves are very real, and not acequately addressed by pure configuration or VM technology.