Yeah, I thought about letting Cullen address your comment but he specifically mentioned that they'd be making the information available for anyone to use and hopefully build upon.

It's certainly not hard to figure out what they're running of course. http://builtwith.com/wpengine.com and the "Net" tab of the Firebug plugin tell most of the story.

Yup, also hardware security devices on the front end -- things like the obvious script hack signs and DoS protection.