I think docker makes sense in some cases, single, compiled binaries that adhere to 12 factor app standards, I'm all for putting in a docker container. I would then run them on a PaaS, if the reasoning is sound. I am working on a project doing this currently.
However, shoe horning something like a php-fpm & nginx stack in there, or anything that doesn't fit the aforementioned spec, seems and mostly is complicated. Doing something like this has caveats, becomes confusing and when you look into it, crazy.
I am fed up of the hype and people thinking that docker is the silver bullet that solves all problems, and should be used for everything.
Ultimately, I feel like a lot of people don't understand how docker works under the hood, and what it takes to deploy and operate applications in docker containers in production. The result of this is mostly scary.
I feel like I don't have to go into details about security, entry point scripts, gosu, multi processes, logging, sketchy build processes, mounting config volumes, persistent storage, layer caches, networking, links, SDN and more. These are some of the things you have to work with with, around or avoid with docker, they are the issues people are not aware of, or don't yet understand.