Parasol Down is usually a place I take out-of-town guests who I want to wow with New Vegas splendor (while still being supremely lazy).
You have to take the escalator down, and the wait for a table outside is typically 10-20 minutes. But you can sit inside and have your first drink, looking up at the gorgeous parasols spinning slowly around...and around...and around....
OK. so. The girl will call your name, give you a seat on the patio...and there you stay for the next two hours. The drinks are steep, but pretty damn good. I'm a fan of the pearasol something-or-other...but have never had a bad drink there.
The real reason for hanging out on this patio though (besides the swanky music piped in and the comfy couches) is the gorgeous waterfall view and the "show" that plays out over the course of the evening. It's quite difficult to describe...there are floating glowing orbs, dancing silhouettes, color shows...words really don't do it justice. Random things come up out of the water, and from behind the waterfall...all in all, a subtle and entertaining backdrop to a great conversation with your guests.