tbh, I see the security point in Docker as a huge risk. Basically you're depending on everyone in the chain to regularly recompile your images or you will get compromised eventually. There is no such thing as an apt-get dist-upgrade or any way to create real useful audit logs with Docker.

On the other hand, deploying stuff is dead easy now. You just tell the hoster "deploy this Docker package, expose port X as HTTP, and put a SSL offloader in the front" and that was it, no more "we need <insert long list> to deploy this" or countless hours spent with the hoster on how to get weird-framework-x to behave correctly.