Nobody knocked on our door or called us checkout day but in all honesty we put the DND (Do Not Disturb) half key in the lock before we went to bed the night before. I like this innovation and find it useful for both the guests and cleaning staff.
It's interesting that so many hotels now have a 4 hour turnaround between check-out and check-in ; used to be a two hour turnaround at least for non resort hotels. Our plane wasn't leaving until 4 or 5 in the afternoon so we (OK...I) packed up everything the night before except our plane clothing, bathing suits and necessary toiletries. Made giving up the the room in the morning pretty painless with only the fridge to clean out before we left.