I wouldn't normally write a review about a chain restaurant owned by McDonalds, but I thought that the following information might be useful for other vegans visiting Las Vegas:
There are a number of vegetarian restaurants in Vegas, but unfortunately they're off The Strip and generally pretty far away from the tourist attractions and tend to close fairly early. The other vegan-friendly options that seem to show up a decent amount on VegGuide are the hotel buffets. Unfortunately, most of these buffets stop serving food by 10:30 PM. Fortunately, Chipotle is centrally-located (right across Las Vegas Boulevard from the Forum at Caesar's Palace and The Mirage) AND it's open until midnight.
I would have probably gone to bed hungry after a long day of travel if I hadn't stumbled across this place at 11:30 PM.