In searching IRV2.com a little I see there have been a number of threads and posts about this campground discount program. I haven't come across much in the way of a comprehensive report about it, however. I'm not saying it isn't there, just that I didn't find one. So I wrote one and stuck it up on my blog.
In short, I've found it very worthwhile. If it is worthwhile or not for a particular person depends on whether or not they use it, and that depends on how often, where and when they go RVing.
I haven't seen much written about the other things Passport America members get discounts on so I've included that in my blog post too.
If you're considering a membership in a campground discount program my blog post may save you a lot of time hunting here and there only to find tidbits of info about PA. My blog, RussOnTheRoad
also has campground and product reports, great photography and photo tips as well as interviews with some of the people I've met on my trip, now in it's 6th month. It's all free, of course, and if you like the blog you can enter your email address there to get notifications when I make new posts.
Find my Passport America report here