While there are some important criticisms in here, there are some misunderstandings of OS-based virtualization with respect to HW-based virtualization in terms of both history and implementation. Certainly, anyone who thinks that "we have reached the point that [hardware virtualized] performance is almost as fast as bare metal" is either cooking their numbers or deliberately limiting the scope of what they are evaluating to purely CPU-bound work; when it comes to anything interacting with the outside world (which is to say, I/O), OS-based virtualization crushes HW-based virtualization.[1] That said, the security criticisms are entirely fair (though they are criticisms of Linux more than of Docker); taken together with the performance win of OS-based virtualization, they form our motivation for Docker containers running as LX-branded zones.[2][3]

[1] http://dtrace.org/blogs/brendan/2013/01/11/virtualization-pe...

[2] http://www.slideshare.net/bcantrill/docker-and-the-future-of...

[3] https://www.joyent.com/developers/videos/docker-and-the-futu...