I just passed immigration at MIA last Saturday.
CBP: where are you going?
Me: Atlanta
CBP: where in atlanta?
Me: Airport Hotel
CPB: what you'll be doing there?
Me: oh, just sleeping
CBP: (raising eyebrows) ...you're going to Atlanta just to sleep?
Me: yes, as a matter of fact I'm doing a mileage run to maintain my FF status
CBP: with which airline?
Me: British Airways
CBP: (stamping passport) have a good day, ma'm.
P.S.
5 minutes from joining the immigration queue to exit customs