I've spent quite a bit of time on this and hoping somebody here can help me save my sanity.
* setup: osx 10.9, python 2.7, pip 6.0.8, virtualenvwrapper 4.3.2 (installed via "sudo pip install virtualenvwrapper").
* problem: global hooks don't work; they are simply not run/sourced.
* investigation: going deeper and deeper into the rabbit hole I ended up pkg_resources. This is used by stevedore "plugins" (used by virtualenvwrapper's hooks_loader.py, used by virtualenvwrapper_run_hooks from the .sh file).
If I understand correctly pkg_resources is blind to the python package virtualenvwrapper (and a few other packages), which in my case is installed in /Library/Python/2.7/site-packages. This, because it looks only for .egg and .egg-info files, whereas virtualenvwrapper is installed (from the PyPI .whl) with a dist-info.
This is when I venture into unknown territory (setuptools, distutils, wheels, eggs, ...) and was hoping somebody might have a clue.