Originally Posted by KLouis

Absolutely wrong, and nobody said this before! If you have three tickets based on three reservations (which is what matio_svk said), you'd have to check in separately for each one, you get three separate boarding passes, and you get miles for each leg! If everything is on one ticket, then, given that the three flights have the same flight number, you do indeed only get miles for that "one" flight. Careful, though: The three tickets may well be much more expensive than the single one.