Last weekend I upgraded my Mac to Mountain Lion. I installed Python 2.7 with PIL and MySQLdb and virtualenv using MacPorts.
When I created and activated a virtual environment with
cd myproject virtualenv . . bin/activate
the PIL and MySQLdb modules were unrecognizible in that environment. What I needed was just different Django versions in my virtual environments, but MySQLdb and PIL libraries had to be shared.
After a quick search I found an additional parameter for the creation of virtual environment:
virtualenv --system-site-packages .
With this parameter I could use my global modules within the virtual environment.