Since then, the company has grown significantly, gone international, and gone public. But I'm pretty sure the "rewards" component has stayed the same. Essentially, you can earn $1 (2,000 points is redeemable for $20 so each 100 points is worth $1) for most reservations. There are some 1,000 point reservations available but they are typically for very early or very late reservations.
I make OpenTable reservations as often as possible. If we're walking around the neighborhood trying to find somewhere to eat, I go on to OpenTable, search what's available and make a reservation on my phone. Sometimes minutes before walking into the restaurant.
Once you reach 2,000 points, it's pretty easy to redeem points for a $20 "dining cheque" that you can use at any OpenTable reservation. Reedeming points is really easy. Login to your OpenTable account, click on "My Profile then "Redeem My Points" and then follow the steps to claim your reward.
It's only $1 for each reservation but it's certainly better than nothing! Don't forget that you can track your OpenTable points using AwardWallet.