How to get there: take the escalators up one level above the main entrance for Marquee / Holstein's / AllSaints. It's the same floor as the all-girls line for Marquee and Jose Andres's restaurant, Jaleo. If you walk straight off the escalator, go to the left of Jaleo. There's no door or sign, just a long hall way (see Yelp photos). If you get to the elevators, you've gone too far.
Anyway, I stopped by around dinnertime for a quick meal. The line moved pretty slowly, and I can only imagine how much worse it probably is late-night when everyone is drunk. There was a 45 minute wait for a whole pie, so we just ordered slices of regular pepperoni. The pizza is good, thin crust, but nothing particularly special. The red sauce pizza is on the blander side, so I recommend getting toppings.
I wouldn't go out of my way to eat here again, but I'd definitely stop by if I were already at the Cosmopolitan and hungry. As far as drunchies, I'm not sure if I could deal with a long wait time, especially with Earl's across the street. Overall, Secret Pizza is not my favorite cheap eats spot in Vegas, since there's nothing particularly remarkable about the pizza; however, it's a nice addition to the Strip.