A Las Vegas Tradition! Me and the Cuz have to have Fatburger at some point between midnight and 5am during every Vegas trip (no exceptions). It's interesting just to people watch and see who comes in at those hours.
I'm a fan of the fatburger and fat fries ... but they have skinny fries as well. I'm pretty simple at that time in the morning/night.
They really have revamped this place ... the outside is a nice lounge-y area now and they have a slushi bar that I haven't tried yet (definitely going to next time).