We used Github Enterprise at my last workplace, paying $5k/yr.<p>We could have easily paid $300/yr ($25/mo) instead if we just used the normal Github site and had a better experience (they were constantly shifting things around to avoid the 20 user cap), but the company IT was adamant on bringing anything in-house that could be brought in-house.<p>Github is great, but there are very few situations in which Github Enterprise really makes sense, IMO.
I believe the biggest complaint I keep hearing about GitHub:Enterprise is it's crappy search functionality. I think a lot of developers want to be able to search the code easily, and Github:E seems to be mediocre at it.