I know for a fact its getting abused, its just to what degree. I have read on these forums as well as others about how people make multiple reservations at several places at once and even at different times so they can "better manage their time and pick that day where they want to eat". So they make multiple reservations at 3 places and end up using one of them, if that. And of course, they don't bother to cancel ANY of them which screws us all no matter how you look at it.
You dont show up, they hold the table for 15 minutes. Then they might sit someone else at it, but the thing is now 15 minutes late as far as schedule goes. If this happens a few times in one day, your 5PM reservation is not really 5PM. You show show up and wait 30-40 minutes for your table since the whole scheduling system is now out of sync. I had to wait 60 minutes at Le Cellier one time even though other people got there 30 minutes after me! It was explained that I didn't have just "any" table at 5PM, its that I was preassigned where I would sit. And if that table was late due to cancellations, slow eaters, etc; I would then have to still wait since that table was assigned to me on such and such date at such and such time. Complete crap if you ask me!
Anyway, I know its being abused and the online reservation system makes it even easier since now you don't have to worry about talking to a human being who might realize what you are doing and give you a guilt trip.