Right now there is an issue with 3 out of the 6 PyPI mirrors being out of date. I have submitted a ticket with PyPI to get them back up to date, but it brings up a good point. Pip should look at the last-modified-date of each mirror and if the date is too old, not use it as a valid mirror.
More information about the PyPI mirrors last modified date can be found here. http://www.python.org/dev/peps/pep-0381/#last-modified-date
I was thinking about writing a patch for this, but I wasn't sure where to start. It would seem like a waste of time to have to check the last-modified-date of each mirror for every install. It would be nice to check only once a day, but I'm not sure how to store the state for this information between installs.
Here is my ticket to get the PyPI mirrors up to date: https://sourceforge.net/tracker/?func=detail&atid=513504&aid=3515219&group_id=66150
Thanks for the report. We know pip's current mirror-selection is inadequate - we have an in-progress branch that uses a more sophisticated algorithm, taking into account the last-modified date, along with some other changes (like SSL and certificate checking). That branch is at https://github.com/pypa/pip/tree/feature/ssl-mirror-requests but still needs significant work.
Closing this issue because #1098 removed the direct mirroring support found in pip.