Kottke (channeling Mark Pastore) tells us that Open Table holds the restaurant by the short hairs, and twists. Ooh, not nice. We don't use it all that often (the best dining in Palookaville, aside from our house, is just around the corner), but it sure can be convenient.
The business model sounds like Quicken's: step into the thoroughfare between provider and customer; provide the customer with a service (mostly) free and squeeze the provider for the price.
Note to self, try to call the restaurant direct.