I took a long hiatus from the arena simply because life got in the way for a while and things were too hectic. Before I left, I remember the forums being packed with posts about G4 & prior to that I remember when G3 hit and how crazy the forums were then. As others have stated, the rise of social media did spread out where other collectors post to.
Honestly, I love the forum format for collecting. It's much easier to search here for past posts and to get information. The way facebook is set up makes it difficult to find a previous post for a particular subject. I belong to a local car club, and let me tell you it is a pain in the butt to try and search for something someone posted even a month ago on facebook. I use facebook mainly for networking as the forum for the car club is almost completely deserted. It's refreshing to see that the arena is pretty active compared to other communities that are/were based on a forum platform outside of social media.
So - while it's not as bustling as it was maybe 7 or 8 years ago, it's still pretty active if you compare it to other collector forums.
I still love it here and I drop in every so often to look and see if there's anything I've missed. It was a nice surprise when the 35th anniversary ponies popped up!