A quick tip when shopping in the US - be friendly to the sales assistant and be sure to use their name during the conversation.
We've just done this and got ourselves a whopping 11% discount at Macy's. Granted, anyone could have got it, all you had to be was a tourist, but what they normally don't tell you is how you go about getting this card - apparently it's normally up to your hotel to give it to you as they don't advertise it's existance anywhere in the shop.
The very helpful assistant said as we're such friendly nice guys, she'd help us out and tell us where in the store we could get one. Apparently we can use it on anything, except perfume and a couple of other things, but she didn't go into too much details. All I know is I've just saved myself a bomb on some Levi's.
I'll definitely be taking my discount card back with me later on this week.