I have used GroupGolfer many times this year. I spend summers in Michigan and winters in Florida so it works out great for me. I saved like $400 on a stay and play for my wife and I in Michigan and I picked up 3 rounds at courses around the Tampa area in Florida, all under $20 a round. I would recommend GroupGolfer to anyone.
As far as the restrictions go there is always going to be an expiration...usually between 3 to 6 months. Many deals have no time restictions but I purchased a couple that were not valid until after 10AM on saturday and sunday...which wasnt bad at all.
Again, GroupGolfer is completely worth the free subscription :)