Won't repeat what's been well covered. It was one of the most exciting experience of my life. Nick was my instructor and was awesome -- was part of a group and one thing I noted is most of the drivers did a great job of teaching to the level of the participant.
Regarding lap times, I overheard another member as his instructor and the answer was: safety. Not knowing people's skill level in advance means telling them on the track makes some folks aggressive beyond their skill level. He did tell me the delta (improvement lap over lap) and you can ask after, they may give you a rough idea. If doesn't satisfy you, do a track day in your own car.
This is a great event for folks doing large event planning in Vegas. It's shorter than a golf round and far more unique.
And I don't like to presume anyone's financial means, but unless you really have a yen to drive a particular street car, skip it and pony up for the F430s. It is awesome.