This year is so much worse than prior years because of when it falls out. You lose between 1 and 3 days (depending on whether you care for coffee at night - motzei R"H and motzei taanis) compared to a different week. If you make sure they scan the cup (some stores they just let you take it and go) it counts as a purchase for 7th cup free. Last year I earned a 7th cup just from the free coffee.