I began using it on my Southwest trip and wonder now what I would do without it. There are thousands of sites in the owner's database and information is added daily. There is also a supplemental invitation-only Yahoo site where the most current files are stored - if you are inclined to print the info rather than use the website database.
Downside? The $24.95 annual fee.
The upside is that for every site you confirm, you get a free week's subscription. I joined in February and my subscription has already been extended till June. I made it a practice to update/confirm every place I overnighted on my way back from Quartzsite.
In addition to the usual Wal-Mart locations, the listings include other retailers like Cracker Barrel, Lowe's, Sam's, Bass Pro Shops, Flying J, etc .... in addition to casinos, city parks, rest stops, and more.
There is also information about where exactly to park, how safe the area appears, how level the lot is, and nearby restaurants and businesses.
I was pleased to add a new site to the tiny town of Ft. Davis, TX which previously had no free overnight listings. With permission from the owner, I stayed for 2 nights in a hotel overflow lot. I submitted the spot, the website owner called to confirm my information with the owner, and now it's on the list. So I feel like I am helping my fellow-travelers.
I consider the website a real bargain and a must-have. I look at it this way, one night in a campground would no doubt cost $24.95 or more.