A list of projects which might serve as useful case studies, with points of contact:

• Disqus (Brett Hoerner, David Cramer) - Powers commenting on CNN.com, MTV.com, Engadget. 250 million users per month, 17,500 requests/sec. they have around 100 servers. See slides on ​Scaling Disqus.
• NASA Nebula (Jesse Andrews)
• PBS (@tarequeh) ​Pluggable applications slides and ​Teaching an old pony new tricks slides.
• ​http://projects.washingtonpost.com (???)
• ​Chicago Tribune ( Christopher Groskopf / @onyxfish )
• Everyblock (Adrian Holovaty, Joseph Kocherhans)
• LexisNexis (???)
• addons.mozilla.org (Jeff Balogh) - Site serves 165 million requests per month. Was previously using CakePHP.
• Cox Media (Chris Heisel)
• University of Texas (Gary Wilson)
• National Geographic (???)
• ​http://politifact.com/ ( Matt Waite/@mattwaite , @jeremybowers )
• Onion (Tom Tobin, Michael Greer) - interview ​http://djangositeoftheweek.com/av-club/
• Mahalo (Jeff Ammons)
• Sunlight Labs (James Turk)
• Nazareth College (@StevenLukeSmith / fvox13)
• Qualcomm
• Compete.com (@roblacy)
• Nasuni ( Jesse Noller )
• Fluther.com - Q&A website with a learning question matching algorithm and a proxied, federated product with some interesting middleware (Tim Trueman/@timtrueman)
• Curse.com - 15M unique visitors / month - ​http://www.youtube.com/watch?v=D-4UN4MkSyI&feature=related Per David Cramer, who used to work there, they are no longer on Django (.Net, part of why he left).