North Carolina started that in '09. I actually welcomed it because we didn't like driving a few hours to find no sites available once we got there. They charge $3/night for a reservation fee, so with more than a 2 night reservation, yours becomes the better deal.
IN and MI have used an online reservation system for years. I love the certainty of the reservation and plus of knowing exactly which site. It's far easier to camp with friends and clubs when you can insure that you are located together.
We've cancelled a few times and lost the reservation fee as a result, but that hasn't happened even once per season.
The one bug I have observed is people willing to pay cancellation fees in order to "book ahead" to claim a prime spot on summer weekends. MI in particular has had to cope with that at the parks along Lake Michigan. So they have changed the rules (full cancellation VS partial) to discourage those attempts.