Hi, I had great success running a Living Social offer when I opened my salon earlier this year - I did two offers, one was for a luxury mani & pedi and the other was for Shellac fingers & toes. I sold just over 80 vouchers and did a 6 month valid to date on them, so still getting the odd couple trickling through now - majority have been redeemed though.
The main thing to remember with them, it's not about you making lots of money, it's about getting people through your door and then retaining their custom.
To help retain them, as well as ensuring they had an amazing treatment (many people complain that when they buy a voucher, they feel they get given a cheapy treatment - this was not the case at my salon) I also gave them a 10% off a next treatment voucher, so that got them back for a second time. By that time, most were loving us, do automatically re-booking!!! Haha!
In my personal experience, I'd go with Living Social over any of the others, especially in terms of their payback to you and customer care (to you as you are their customer) Good luck, xx