'NSA uses Python for cryptography and intelligence analysis.'

...and...

http://www.python.org/about/success/usa/

There's also a list of other companies using Python I didn't mention in my earlier comment. That was a session speech given by Wesley Chun, author and long time programmer for Python and current Google employee along with the founder of Python, Guido van Rossom, at this year's 2011 Google IO conference.