why spend time
"why spend time, energy and money virtualising more than you have to?"
Because in many cases using containers would require much more time, and energy(as in human energy, and thus money) to manage than virtualization.
I have 6 containers deployed at my company for a *very* specific purpose(3 hosts w/2 containers per host each container runs identical workload). They work well. They were built about a year ago, and haven't been touched much since. I have thought about broadening that deployment a bit more this year, not sure yet though. I use basic LXC on top of Ubuntu 12.04, no Docker around these parts. Adapted my existing provisioning system that we use for VMs (which can work with physical hosts too) to support containers.
Containers are nice but have a lot of limitations(lack of flexibility). They make a lot of sense if you are deploying stuff out wide, lots of similar or the same systems, in similar or same configuration (especially network wise). Also most useful if you are working in a 'built to fail' environment, since you are probably not running your containers on a SAN, and unless things have changed containers don't offer live migration of any sort. So if I need to upgrade the firmware or kernel on the host the containers on the host all require downtime.
So for me, 6 containers, and around 540 VMs in VMware.
I've had one vmware ESX host fail in the past 9 years(my history of using ESX, used other vmware products too of course - in this case it was a failing voltage regulator), Nagios went nuts after a couple of minutes, I walked to my desk and by that time vmware had moved the VMs to other hosts in the cluster and restarted them(had to do some manual recovery for a few of the apps). I don't think that happens with Docker does it? (you don't have to answer that question)