Sorry to bump such an old thread, but wanted to add a little to the collective wisdom of the TexAgs Vegas knowledge base...
Just got back from a couple days in Vegas for March Madness. Got to town Thursday afternoon. Walked down the strip, sports books at Ceaars, Bellagio, Cosmopolitan, Aria were SRO. Finally headed back to where we were staying. The book at the Mandalay had far more seating, most was occupied or reserved. We finally found a couple of empty seats and parked for a few hours. Seems most seats get "reserved" by 7:30-8 am...a group sends one guy down who stakes out some seats and puts a piece of paper with "reserved" written on it. Everyone seems to respect that. Everyplace seemed to have quite a few seats officially reserved by the casino. Unless you have someone willing to be in the book really early, I'd recommend calling the sports book and seeing what they can do to help.
The lines to make a bet had huge fluctuations, 50 yards long or so at times, 3 people long at others. If you're making a bet, try to do it early to avoid standing in line.
The book at the Mandalay needs to upgrade their televisions badly. Otherwise, I thought it was a good place to watch games and lose some money, and offered a decent chance at getting a seat.