From what I can see on an upgrade anyway, they don't seem to be enabled by default, but not hard to setup (I did a quick note for ubuntu https://raesene.github.io/blog/2016/02/04/Docker-User-Namesp...)

Yeah, there is a pretty sweet blog post and demo videos (just posted) @ https://blog.docker.com/2016/02/docker-engine-1-10-security/

> Wow, user namespaces! That was quick!

Heh. Yeah, it took quite a while. Lots of kernel bugs. :P