bedelman - Just want to say that the 72-hour thing is the way I understand it. I have not used the tourist card myself, so you should reconfirm with the ticket agent. The AE is too expensive for me, and the travel card doesn't seem that good a deal to me anyways.

Anybody can ride the shuttle buses run by MTR/Airport Express. I've heard of locals riding them, even though they are not going to/from the airport at all. One downside is that they are pretty infrequent.