First and foremost, my advice is to GO EARLY. Huge lines if you arrive past 11:00. At that point, don't even bother trying to get in unless you have the hookups or you're coming with supermodels. Also, they told me two hours before it opened that it was $30 for entry but when I got there that night they charged $50. I was really pissed at first but by the end of the night I felt it was completely worth it.
This place is just ridiculous. The outdoor pool area is huge and you can actually put your feet in if you want to sit and cool down. There are also random jacuzzis around as well if you want to stay warm. If you walk past the pool, there's a gazebo where you can gamble as well if you're tired of the clubbing scene. There are just so many things here that look amazing it would take me two hours to write about all of it. I hate using cliches but it literally looks like a movie set.
One bad thing about XS is that the bars are ALWAYS jam packed. It seriously takes you 20 minutes to get a drink. My advice is to befriend the people who get bottle service and get some alcohol from them. Bring some random girls for them and you're in for sure.
This leads me to my next topic which is girls. There are so many gorgeous girls here it's ridiculous. I used to be very active in LA nightlife and even then, I have never seen anything close to this many hot girls in one venue.
What made my night was that everyone here was so cool (probably because they're in Vegas). Even when some Australian guy caught me stealing vodka from his table, he got mad for 2 seconds and then just laughed it off and said "It's ok mate!" as I continue downing his drinks.
If you've never been here before, I highly recommend you go... I went to a few other clubs in Vegas and nothing is even half as good as XS.