So if you're using virtualenv 1.7 and are wondering why you can no loger see your global Python site-packages directory it's because the default behavior has changed.

Now the default install for virtualenv is to hide site packages; equivalent to passing the old --no-site-packages command:

virtualenv --no-site-packages <env>

Since this option is now default it's no longer needed, and the new command to see the global site packages is --system-site-packages:

vitualenv --system-site-packages <env>

Hopefully this saves you some confusion as it's not clear what's happening when your new install now suddenly is breaking.

Virtualenv and pip install typically go together so I'm combining their cheatsheets. These are the commands I use the most. This is pasted here for quick reference.

# create new virtual environment
virtualenv <name>
virtualenv <name> --no-site-packages

# activate and deactivate virtualenv 
source <name>/bin/activate
deactivate

# pip install
pip install PACKAGE
pip install PACKAGE==VERSON
pip install PACKAGE>=VERSION
pip install PACKAGE --upgrade
pip install -r /path/to/requirements.txt

# pip uninstall
pip uninstall PACKAGE

# pip freeze
pip freeze > requirements.txt

# pip install tar bundle
pip install http://example.com/path/to/tar/package.tgz

# git
pip install -e git://github.com/user/MyProject.git#egg=MyProject
pip install -e git+http://git.myproject.org/MyProject/#egg=MyProject
pip install -e git+ssh://git@myproject.org/MyProject/#egg=MyProject

pip install -e git://git.myproject.org/MyProject.git@master#egg=MyProject
pip install -e git://git.myproject.org/MyProject.git@v1.0#egg=MyProject
pip install -e git://git.myproject.org/MyProject.git@da39a3ee5e6b4b0d3255bfef95601890afd80709#egg=MyProject

# mercurial
pip install -e hg+http://hg.myproject.org/MyProject/#egg=MyProject
pip install -e hg+https://hg.myproject.org/MyProject/#egg=MyProject
pip install -e hg+ssh://hg@myproject.org/MyProject/#egg=MyProject

pip install -e hg+http://hg.myproject.org/MyProject/@da39a3ee5e6b#egg=MyProject
pip install -e hg+http://hg.myproject.org/MyProject/@2019#egg=MyProject
pip install -e hg+http://hg.myproject.org/MyProject/@v1.0#egg=MyProject
pip install -e hg+http://hg.myproject.org/MyProject/@special_feature#egg=MyProject

# subversion
pip install -e svn+http://svn.myproject.org/svn/MyProject/trunk@2019#egg=MyProject

# bazaar
pip install -e bzr+http://bzr.myproject.org/MyProject/trunk/#egg=MyProject
pip install -e bzr+sftp://user@myproject.org/MyProject/trunk/#egg=MyProject
pip install -e bzr+ssh://user@myproject.org/MyProject/trunk/#egg=MyProject
pip install -e bzr+ftp://user@myproject.org/MyProject/trunk/#egg=MyProject

pip install -e bzr+https://bzr.myproject.org/MyProject/trunk/@2019#egg=MyProject
pip install -e bzr+http://bzr.myproject.org/MyProject/trunk/@v1.0#egg=MyProject