And for everything else that is just data processing in the stack, ephemeral storage isn't a bad thing (stops developers writing things to disk when they shouldn't).
Of course, but how? Can a docker container somehow write to the host fs? It couldn't, a few weeks ago.
[1] https://github.com/dotcloud/docker/wiki/Docker-0.5.0:-extern...
Which may or may not be the host machine, and most likely would be the machine you configure to be next door with more focus on SSDs than CPU.
I also figured, but haven't checked, that Docker will eventually support Vagrant-style shared folders. But maybe this breaks the philosophical design of a container.
As LoonyPandora said below, apparently they added shared folders recently, so I'll play with that today.