My wife has one, and we take full advantage everywhere we can. We spend most of our camping nights at CoE parks. They are quite nice and around here they are upgrading to sewer at the more popular ones.
Youroo is correct, if going to a National Park item everyone in the group gets in for free.
2011 Ram Truck 2500, Crew Cab, 6.7L CTD, 4X4, 3.73 Rear