I usually check out by phone or even using the TV, so stopping by the front desk merely to pick up my Bonus Bucks is a totally unnecessary inconvenience -- and I may not have time, frankly.
Just as an experiment, I checked out in person this morning from the Detroit Airport Marriott. It was 10:45 a.m. The person at the front desk was a stranger to me. I walked up, handed her my keys and said, "I'm checking out of Room 427." She asked if the bill that had been put under my door was correct. I said that it was. She told me to have a nice day, and I was off. I doubt very much that she knew I already got my Bonus Bucks. But she happily let me walk away without ever mentioning them. That's another reason I want them at check-in: so neither I nor the hotel can forget.
Bruce