You are going to have a blast!! Las Vegas is one of my most favorite places to go. It is very kilt-friendly there, too. My wife and I spent a week in Vegas in Apr. 2007, and I did not pack any bifurcated garments at all. Aside from a few odd looks all I got was positive comments.
One word of warning though...be very careful when going over the air vent grates in some of the sidewalks. Don't ask me how I know. LOL