On a trip this summer, I had the itinerary: LHR-EWR-SFO. I got off at EWR, never boarded my second flight, and ALL the miles have been posted.

I would not try this where you fail to take both flights, for example. Also, on domestic flights, collecting boarding cards does not translate directly into a check of the passenger list. Why? Just look at the procedures -- at 5 minutes before closing the door, they just count empty seats and let standbys on the plane. If they were really checking each passenger, they would know exactly how many seats are available.