First off, what people say about R.com here are all true. I'll try to share everything in bullet points.
Good: If the restaurants accept it, then it's worth the price you pay
Bad: Not all restaurants accept R.com certificates. Call in advance or simply pay before you eat.
Good: After your first purchase, you will get promotions such as $25 certificate for $4 or five $25 certificates for only $20. (it's still a good deal)
Bad: Be careful, they do NOT refund the purchase price regardless what the reason is.
Good: They list all types of restaurants, from American to Asian, to Mexican.
Bad: Their "distance" is bogus. I searched restaurants within 15 miles within the vicinity and the results even listed restaurants 25 miles away.
Good: No expiration date on the certificates
Bad: Don't matter. Sooner or later, either the restaurants refuse to accept these certificates, or they stop their "contract" with R.com
From experience, restaurants normally charge a gratuity or "extra" tax if you decide to use R.com certificates. (not mentioned under Terms & Conditions). Overall, I'm satisfied with R.com, but based on the hundreds of reviews I read, R.com is not on anyone's side. Not restaurant owners or consumers. They're there to make money from both ends. They are more of an online restaurant advertiser.
I can't say they are a scam, but I definitely can't say they are good to use. Use it at your own risk!!!