I believe at one time restaurant.com was a useful tool, but that is no longer the case. Hardly any restaurants seem to participate anymore, at least in northeastern Pennsylvania and Philadelphia. There are a handful of restaurants listed in Philly, in the far northeast.
The other consistent problem is going to a restaurant listed as participating on the site and AFTER REDEEMING only to find out the owner no longer accepts the vouchers.
I assume the company will fold soon, unless it is successful in very specific areas.