Wear really comfortable walking shoes.
The Amazon Room is big, but it's not really THAT big. I found the hallway to the Amazon Room to be what requires the comfortable shoes.
To the OP, when I was at the WSOP in '06, I left right before the Expo started, so I can't tell you about it first hand. But I hear they have alot of neat poker related things there. The Expo is in the same general area as the WSOP (Amazon Room), so you could spend an hour or two at the Expo and walk down the hall and actually watch the WSOP. It's a good setup and I definitely recommend that poker fans make the trip at least once.