We stayed at a former (as of Jan 1 2014) KOA in Fond du Lac, WI, in early August. It is a lovely campground, with some seasonal sites, which are very well maintained. Owners were very competent and helpful.
They told us they had basically no benefit from the KOA branding, plus the fees were way too high. It's the only full-service RV park in a 30+ mile radius, so people who want their amenities are going to be there. Also being on the lake, they have a high demand for seasonal sites and a large repeat business from people coming there to for fishing and boating.
BTW, it's Breezy Hill RV Park, just outside Fond du Lac.