I work at a company that leverages Hadoop, and on each developer machine we each have a baby Hadoop cluster (3 nodes) running in VMs at the moment, in addition to a master controller. Hence, at any given time, my machine is actively running 5 OS's (if we include the native OS) and all their associated background tasks. My computer generally idles at 25% CPU usage. Keeps my legs warm in the winter.
We're finally going to dockerize the project and I couldn't be happier. Granted, Mac OSX doesn't natively support the LXC's docker uses (c'mon Apple!), so we'll still be running 1 VM, but that's a huge improvement over our existing implementation. My CPU wouldn't be idling nearly as high, I'm going to recover a ton of RAM, and the boot sequence is going to be substantially faster.
Being that these are developer machines, and simply understanding our use case, we're not worried about malicious tenants breaking out of their environments. It's just not a factor in our situation.
If anything I feel the "article" was a waste of time. I thought I was going to read a great summary on the state of Docker, and instead I got this unexpectedly aggressive piece from developer that couldn't conceive how to fit this particular tool into his toolbelt.