I used to be.
It was a ton of fun, but my little Paint was having trouble with the big solid XC jumps, by the time I got around to getting my D-3, so I dropped out. Our club mainly focused on jumping, very little dressage or games, and at the time dressage was my main thing. There were some friends horses that I could have used for it, but I just didn't find it worth it, if I couldn't do it all on my own horse.
I miss it sometimes, but I'm involved in plenty of other organizations to keep myself with things to do.
I loved the rally's, and parties, and all that fun stuff with the friends, but as others have said it gets very political, and sometimes it's enough to stop you.