I used google places in another business. Changing the offer frequently is important. Didn't get alot of traffic the first few months, but after 3-6 months of consistantly offering coupons, we started seeing activity from the free posting. Sometimes free is worth what you pay for it, nothing, but sometimes you get a new customer. As we all know it costs way more to get new ones. Free except for a little bit of time is not a bad deal if you even get one new customer out of it.
I wouldn't presume to say the business I ran relates at all to this industry but having had experiences with Google Places/Maps it is worth the little bit of effort to get a new customer.
The ones we got had in fact been to our web site, and read reviews of the business. However, they didn't act until they saw a coupon when searching out our competition on the map.