If you are using pip install somepackage, and it is not going into your virtualenv, perhaps you are tripping over the same thing I did.

I had activated the virtualenv with /usr/local/pythonenv/DJANGO-1-1/bin/activate, and (DJANGO-1-1) was appearing in the shell prompt. which pip showed /usr/local/pythonenv/DJANGO-1-1/bin/pip. python followed by

import sys
for p in sys.path:
    print p

showed that the system site-packages directories were not being included. So why was the python package being installed to /usr/local/python2.6/site-packages???

Well, the pythonenvs had been installed as root. I was actually running sudo pip install somepackage and that meant I was losing the virtualenv environment (which sets some environment variables that don’t survive the sudo to root transition).

So the solution was to run [UPDATED 2011/01/04]

sudo /usr/local/pythonenv/DJANGO-1-1/bin/pip install -E /usr/local/pythonenv/DJANGO-1-1/ somepackage

and indeed I threw in the --download-cache option to cut down on the download time (although I subscribe to DSL, my download times are closer to dial-up speeds) for subsequent installs into the DJANGO-1-0 and DJANGO-1-2 virtual envs.