I've been using OpenTable for years now, and I love it. It's great to be able to make an online reservation without having to wait on the phone, say your name twice, hear that there are no reservations actually available.
Unfortunately, lately there's been a trend of restaurants calling to confirm when I make an online reservation. I get it. They don't want to be stood up. They've probably been burned multiple times before by people who make online reservations and then turn into no-shows.
The only problem here is that OpenTable is an online service with a database. They should be able to tell a restaurant how reliable a customer is (I've never missed a reservation before). If the customer has missed one or two reservations, sure, call that customer to confirm the reservation. If the customer has missed more than two, don't let her make online reservations any more.
With an online database, this shouldn't be too complicated.