As an ex sysadmin I really like the container infrastructure. Manage the whole configuration on the main machine with puppet and deploy the blackbox applications (everything ruby and java related) with docker/rocket.
I can't remember what the application was, but I've seen an application where the only installation instructions where for Docker. That's just plain silly.
My concern with containers is that the wrong people will use it. There is a ton of software out there with just barely runs and make all kinds of assumption about it's environment. I fear that rather than design better, more correct software, these people/companies will start packing up their development environments as containers (more or else) and just ship those. Of cause that's no reason to discourage the use of containers, we just need to be critical of what is inside them.