I've gone twice, and both times were for friends' birthdays so I've only dealt with the advanced line. We waited 10-15 minutes and then got right inside. Security wasn't bad, got patted down but no groping went on. First time around the security woman threw my gum out but it wasn't a big deal (I was drunk though - at that point all I cared about was getting inside to pee).
I paid $20 the first time, and $10 the second. I've only been on three floors so far: the main floor (electro/techno music), the "Funky Room" which apparently either has its own music (top 40/hip-hop) or music from the main floor, and Pachita (hip-hop). I had fun on all three.
The last time I went, the crowd was pretty good - a lot of well-dressed and decent people. However, you do have the exceptions since the dress code is actually kind of lax. A LOT of guys but that was okay - more choices for me. But with that said, some of them are creepy and/or aggressive. I was heading to the staircase up to Pachita and some guy grabbed my ass. By the time I turned around to react/snap at him, there were too many people between us.
Basically, find a way to get a cheaper cover price (to be honest, I'm not so sure if I'd be willing to pay $40, even though I did have mostly positive experiences there [then again, I'm a nearly broke college student]), go with people you know you'll have fun with, be open to meeting other people, pregame if necessary, and don't let little things ruin your night.
Downsides: When there are a lot of people, it gets really, really hot so you'll want some water to drink BUT regular plastic water bottles are $5; the guys can be grimy.