I think the more appropriate question as to whether or not the service is "worth it" to a restaurant operator is: does Open Table give you access to customers that would not pick up the phone and call you for a reservation?" AND: "are those customers that have the potential to become 'regulars," and by virtue of them coming to you by Open Table (and accessing their profile), you now know more about them on their first or second visit than other new customers and therefore you can build a deeper relationship with them, more quickly?"
Alternatively, does Open Table give you the chance to fill seats on a slow night that might otherwise have gone unfilled, by virtue of the fact that someone can search for a restaurant in Louisville for a reservation tonite, and see that you have tables open at a convenient time compared with their other options? What are those customers worth? (or what is it worth to you fill those tables, assuming they'd not be filled by other means? Or, to ask a different way, how many calls per night do you get from people just checking if you have availability?).
That's the marketer/business person in me. As a consumer, I don't believe that Open Table takes away the relationship from the restaurant at all - let me relay a story from this past Sunday night as a perfect example: I was in NYC on business Sunday - yesterday. I didn't have dinner plans for Sunday night, so in the car from the airport, I went on my phone and searched Open Table in the 4-5 neighborhoods that I knew were adjacent to my hotel. I just wouldn't have called, as I didn't have any way to narrow things down as effeciently as the site does for me. That narrowed my choices to 3 restaurants. From there, I looked at the menu portion of the site, and the diner reviews (I have found that the reviews on Open Table tend to be more reliable than the citysearch, trip advisor or zagat/gayot sites). "Hmm, never heard of this restaurant, or the chef, but the write-up they provide the site themselves sounds interesting , three pretty recent reviews, all raving...." OK - I'll try this place." Made the reservation. The restaurant, Gentleman Farmer, was a 20-seat restaurant on a primarily residential street on the Lower East Side, and unbenknownst to me, had only opened 9 weeks ago, so I would never have found it otherwise. They greeted me by NAME when I walked in, knew that I was dining solo, so specifically asked me which of 2 tables I preferred (and recommended one). From that point on, I had an amazing dining experience, which had nothing to do with Open Table, and everything to do with their own service and how they treated me. However, it was Open Table specifically who delivered me to their door, and gave them the information to help set the positive tone from the start of my dining experience. My $60+ check (I ordered a bottle of wine, so sue me

was 100% due to the fact that the restaurant was on Open Table, (although my 25% tip had
everything to do with the restaurant's service).
I have no personal stake in Open Table or anything of the sort; I just would like to have more restaurants on Open Table for my own convenience, since I use it so often

(and yes, I also use it in Louisville pretty extensively - again, because it helps me to see at a glance what restaurants have availability when I am dining on short notice)
Just my 2 1/2 cents....