Or lead generation for restaurant customers?
OpenTable/Groupon has an advantage there since they have a very direct method of measurement.
That's not to say that it's a bad idea, just that it wouldn't change my recommendations, personally.
Restaurant online ordering providers usually fall into two camps:
1) Simple ordering that goes to email, fax, or phone. There is no integration with the kitchen and restaurants have to reconcile their reporting at the end of the day.
2) Online ordering website integration directly with the restaurant's point of sale system. This works better for the restaurant cause the orders can go straight to the kitchen printers, the sales reports are all in the same place, and the orders pop up in the point of sale system that the restaurant is already using. This is a lot more work (and a lot more expensive), and first you have to convince the POS manufacturers to give you access to their APIs.
Additionally, not all restaurants are interested in doing online ordering (it affects the workflow of the kitchen to have orders coming in 'out of band').
I wouldn't want to limit our service to only folks interested doing online ordering, but it might be an interesting add-on for us down the road.
Or roll your own POS and blow the competition completely out of the water. :-) There is a huge opportunity here for the sorts of people that hang out on HN.
On top of this, the hardware used by these POS systems is absolutely terrible. The "new" hardware used by wait staff is basically a Blackberry with a tiny screen and a stylus which is easy to lose, sold by Symbol. The menu functions on them are complicated, and last I checked, the replacement costs rival a new iPhone.
...and there's a device out from Apple which attaches to the back of an iPhone and allows users to swipe credit cards through the iPhone. (Sorry Square, I really wish you had responded to even one of my emails, but it looks like that bus has left the station now.)
With competitors like these, you should be able to pretty successfully market a replacement using commodity hardware, open systems, and a yearly "support contract" that would entitle the customers to upgrades, etc.
One of the vendors, "Digital Dining", has only just recently started offering integration of menus into their customer's websites, and it's clunky as hell.
Your bigger challenge would be getting existing restaurants to convert. Once they pay out for one of these piles of crap -- and get it working after weeks of aggravation -- they're reluctant to do anything that might upset it.
But businesses like mine would be very happy to guide them through the transition. :-)
edit: You already know all this. But maybe someone else doesn't.
We think it's worth the time and the money, and we agree that the current clunky, antiquated hardware and counterintuitive software is a disgrace. It's one of those ideas (upgrading restaurants) whose time is fast approaching.
I think maybe you are overthinking that aspect of it. I totally understand and likewise agree with doing POS integration with the kitchen(you can't automate it), but there are methods already present in every restaurant to getting an order to the kitchen, some are paper, some are DASH(Darden's system, microsoft stack) aloha system etc seems to be a pretty big one.
I think skeptical restaurant owners would choose that no-risk option, and you'd probably make more money. Restaurant owners who think it'll be successful in making sales would probably be willing to pay a decent sum per month.
I agree with the other commenter that you are probably not charging enough. I think this kind of service has high value if it can demonstrably increase sales.