Russell Pavlicek from the Xen project asks "Are Containers the Right Answer to the Wrong Question? on the Citrix Open@Citrix blog. While Russell brings up many good points, including both Mirage OS and OSv, I believe his article misses the mark about where and how Linux containers are changing the way we do IT. Its true that containers are more limited than full blown virtual machines, but the real magic is about process and management.
The operating system of a server is both essential and completely besides the point. The choice of operating system can have a major affect on the structure and management of your application, so it is absolutely necessary to consider the OS family, flavor, and version carefully when planning deployment. But the client never sees the operating system. The web application that they interact with never (or at least, shouldn't) give an indication of the operating system powering it. So, in that way, the OS doesn't matter, it simply needs to be there and it needs to work flawlessly.