I've used it 3 times now. Works like a charm. Be wary of the minimum purchase requirements though...you'll end up spending the same amount as you usually would just trying to get to the minimum.
The other day TechBargains.com had 60% coupons on ALL Restaurant.com coupons. I went and found a restaurant near here that had $15 coupons. The grand total was $1.00 per $15.00. So I bought 3 of them for $3.00. We went to the restaurant and ordered a regular meal which came out to be $15.60. My total was $.60, plus the dollar I paid so $1.60. Plus tip was $4.60. A philly cheesesteak plus a calzone plus fries and 2 drinks for $4.60 including tip is a steal if you ask me.
Just make sure when using the coupon that you don't spend over the minimum amount and that if it has a huge minimum amount, bring 3-4 people with you.