A few thoughts on this, firstly you are right to an extent - Docker doesn't give you portability completely due to binary dependencies, but if for example I wanted to move my app from the same major version of CentOS or RHEL on a virtual machine to something running with the same major version in the cloud it should be relatively straightforward. You are right though that this won't work going from something like Ubuntu to Suse for example.

LXC currently has a gaping hole around security because it doesn't use SELinux - you might want to read this article: http://mattoncloud.org/2012/07/16/are-lxc-containers-enough/

The key bit is that we are starting to converge on a standard container for the Linux OS and with Red Hat working to get things working with SELinux we should have a pretty awesome container for our apps.

Finally, Docker adds a lot more on top of LXC, which is why people love it so much - you can see a comprehensive answer by Solomon Hykes here: http://stackoverflow.com/questions/17989306/what-does-docker...

Given the above I'd rather standardise on an Open project that adds a lot more value to LXC and hides that complexity away and given the largest linux vendor is putting it's weight behind this I'd say this is rather awesome!