I have it stated in my handbook that parents who are late will receive ONE verbal reminder. After that, they will be charged $10 per half hour, or portion thereof. And I think that's kind of generous. I had to warn one family that I could not continue care if they were not able to pick up their child on time. They got better, but let me tell you, I was not sorry to see them go when mom went on mat leave.
10 HOURS, PEOPLE! You have 10 hours to come and get your child!! MY time, with MY family is no less valuable, just because I am in my own home. Take it seriously, PLEASE.

Yes, this is an area that bothers me, as well. Luckily I have a great set of parents currently, who are respectful of my time. I am willing to be a little more lenient with those type of people.