I have had a great traditional carbonara at Spago for lunch but it is off the menu. Another rendition is the black pasta carbonara with lobster at Valentino. It was good but I have had better elsewhere (not in Vegas).
Was it classic Carbonara tossed with just cheese, egg, pancetta or more the cream-sauce Carbonara that many places are serving? If you want the classic, try Trattoria Reggiano in the Venetian Hotel . And oh, they have the best garlic rolls!
The one at Martorano's had a little cream in it and they served it with an egg yolk on top which the waiter tossed at the table. What I really like is eggs, cheese & pancetta like I had at a restaurant in Venice (twice)