Most deployment systems depend on PyPI, the Python Package Index, for fetching and installing dependencies. Although performance and reliability has greatly improved, there are still days when you may find PyPI down and thus are unable to deploy through the normal fashion.
Finally, there is now a concerted effort to create official mirrors of PyPI that everyone can use (see PEP 381). The mirrors are pretty simple--they're not full blown package indexes--and you can already start using them for experimentation. Also, thanks to Richard Jones, Martin Löwis, Guido, and others at EuroPython, my half-baked idea of using Google App Engine as a PyPI mirror has been resurrected! I don't know if it's fully implemented yet but you can try it out at pypi.appspot.com. App Engine seems like a logical place for a mirror due to its scalability. However, I am skeptical of how well it will perform. App Engine still has a long way to go with regards to stability.
To get involved with the mirroring project you can follow the discussions on the Python Catalog SIG mailing list. The next step will be modifying clients to discover and fallback on available mirrors.