The Expo that is going on at the same time as Macworld is the United Motorcoach Association Expo. I saw the sign in front of Moscone North that detailed their hotel shuttle schedule. It listed the hotels it goes to and one of them was the Marriott. You have to be real lazy to not walk from the Marriott to Moscone. It is a 3 minute walk and just over a block. You’d spend more time getting onto and off the bus than walking.