I have monitored the offerings of http://www.GroupGolfer.com in Michigan. I first learned of this outfit at the Michigan Golf Show and Golf Blogger did a little piece on their concept following the show. They operate in about 1/2 the states and each state has a separate offering, good for 2-3 days.
I finally bit. They were offering 18 holes (including cart and range balls) at the Grande Golf Club for $25. The limitation is that the certificates are not valid from 8am to 11am Friday to Sunday. The certificate expires 8/1/2011. I am always a bit leery of these deals. They typically compare the certificate cost against the highest mid-season weekend rate. Right now in Michigan, most courses offer deals without the bother of ordering through a web service.
In the case of the Grand Golf Club, their mid-season weekend rate after 1pm is $40 and mid-week Senior rate is $35. The deal is good but not necessarily great. Once things dry out a bit from our April showers, my stepson and I will make the trip to Jackson and see if the certificates work! (watch for the expiration date. Some of the offerings have relatively short expiration dates).
I have tried http://www.lessonongolf.com successfully in the past and my recent trip to San Antonio showed that GolfNow can be handy ($140 rounds at La Cantera Resort for $75 each). We will see how GroupGolfer.com ultimately stacks up.