Who is "we" ? I had the impression unikernels were still a highly experimental work in progress you could only use with ocaml and that noone had ever used in production for anything serious.
It's beyond experiments now and there are clear uses for such things. For example, a recent post describes using MirageOS to build a firewall VM [1]. There are also network security/intrusion-detection systems [2].
There are a number of ways to build unikernels and they're not all OCaml (which is just MirageOS) -- http://unikernel.org is trying to bring these together.
Yes, of course. I should also have linked to the Unikernel+Docker demo [1], which is taking legacy software and using Rump Kernels and the Docker toolchain to deploy unikernels (to show how all these things can create a multiplier effect in terms of benefits).
It would be great to get a list of live unikernel deployments listed somewhere to address questions like this when they come up.
Most people run VMs for hardware utilization purposes.