I've used them with quite a bit of success in the past. Ever heard of Ebates.com? They allow you to connect to outside sites, but in return you get extra discounts and cash back. I've had times where I've gotten $100 in Restaurant.com coupons for only $15 and gotten cash back when ebates sends out a check.
(Just to plug it, if you wanna try out ebates use my email [danielcartis at gmail] as a referrer and we'll each get $5 bucks)