Unfortunately I didn't have more time to work on it so it is basically unmaintained, but every now and then I still use it, mainly when I need to install software on machines where I don't have administrative privileges, and it works great. I wish I implemented some kind of dependency handling mechanism, it would have made it much more useful.
In particular look at the `conda package` command for an easy way to bundle up any non-conda packages across a homogeneous environment.
virtualenvs are just overrides to environment variables that change where things should look to find the python interpreter, libraries, modules, et al.
docker is much more involved, using LXC to force process isolation, an effective chroot, networking restrictions, etc.
many (most?) folks' current usage of virtualenv would not be portable to docker without substantive work to accomodate the restrictions that docker imposes.
(note: this isn't a critique of docker; those things are features. they're just orthogonal to this)