Made it just in time for the lion feeding today. The trainers throw meat against the windows and the lions come around and eat off the windows while you take pictures and gawk. There's also a walkway where you can walk right underneath the lions. Inside the walkway is another little room where you can take a picture with a lion cub for $25 (!!). It's a really cute cub though. ^_^
The presenter said that the lions sleep 18 hours a day, and the lions are changed about every 6 hours or so (rotated in from a ranch off the strip that has some 20+ lions).
Definitely a must-see when you come to Vegas.