Earlier quoted context omitted.
It comes from Cal Henderson's DjangoCon 2008 keynote: http://www.youtube.com/watch?v=i6Fr65PFqfk&fmt=22#t=55m1... He jokingly said Django needed a mascot and that he could take a framework seriously if it had a mascot with magical powers.
And then, to answer the criticism, the community came up with the pony: http://djangopony.com/ And then to complete the cycle, the pony showed up to conferences, where it was much loved: http://www.flickr.com/photos/ubernostrum/3919450494/in/pool-... Lately it's retired a bit since the joke has run its course. Not sure what the next one will be.
The novelty has and will continue to wear off, but the Pony won't be going away. Once an unofficial mascot, always an unofficial mascot!