We implemented a "mega box" drop down at the University of Nebraska (http://www.unl.edu/) in 2009. We didn't do a production a/b test but we did do in-person a/b testing using a custom web app that tested user's ability to find things in the navigation in the mega box compared to a traditional flag model. Mega box won.
Also note that this nav and template isn't unique to the homepage like most higher Ed institutions but is used site wide by all units. That was an epic battle story for another time.
thanks for the info, i'm currently working on a redesign from a site that has all of the top 2 levels of nav showing in a side bar and the proposed design has a single level with "mega menu" style dropdowns, I'll bring this solution up as an option we can focus group. Also, I like the ability to pin the menu open, nice touch
Also note that this nav and template isn't unique to the homepage like most higher Ed institutions but is used site wide by all units. That was an epic battle story for another time.