The html docs installed with matplotlib include code that calls http://sourceforge.net/apps/piwik/matplotlib/ when you browse them and slows down loading the pages.
Created attachment 234335 [details, diff] stop piwik code being added to html docs
Patch in cvs. Could you report your patch upstream as well? Thanks!
New patch created to make the piwik code optional (I guess the matplotlib folks want it!) and submitted on: http://sourceforge.net/tracker/?func=detail&aid=3015217&group_id=80706&atid=560722