I am getting
IOError: [Errno 13] Permission denied: \'/usr/local/lib/python2.7/dist-packages/python_dateutil-2.2-py2.7.egg/EGG-INFO/top_level.txt\'
I was just having similar issues on my machine. Pip wasn't letting my install anything because nothing could be written to my site-packages directory. Not in love with this but I ran sudo chown -R $USER /Library/Python/2.7/site-packages/
and now Pip has no problem writing to my site-packages directory.
In my case:
sudo chmod o+r /usr/local/lib/python2.7/dist-packages/python_dateutil-2.2-py2.7.egg/EGG-INFO/top_level.txt
In general:
sudo chmod o+r [XXX]
where XXX is the file it is pointing to.
This is a known issue with python-dateutil where the permissions aren't set correctly in the pypi package: https://bugs.launchpad.net/dateutil/+bug/1243202. This isn't a problem with pip because pip normalizes permissions, but if you install it differently you might run into problems.
The easy solution is to run
sudo chmod o+r /usr/local/lib/python2.7/dist-packages/python_dateutil-2.2-py2.7.egg/EGG-INFO/top_level.txt
and the same command on any other file you encounter with this problem in the dist-packages directory.