Not being much of a social person, I've never had much interest in the social aspect of Facebook, but being naturally inquisitive, I have my own account there just to kick the tires, so to speak. I think the clean design and the API library were appealing at first. But shortly after, the novelty wore off and now I barely login anymore.
What I have also noticed with Facebook fans is that many have started to de-friend each other, the process of removing people from friends lists. I suppose it's the same with real life, friends and acquaintances come and go in one's life. The virtual world is probably no different.
But there are a couple of subtle differences with Facebook. Firstly, when people initially joined the network they added anyone and everyone they knew, some to reconnect, others to help raise their social status ranking. Since then many have realized that they don't want to openly share aspects of their lives with everyone. This brings me to the second difference. With Facebook, a person uniformly shares his/her private posts with everyone in their list. That's hardly similar to the real world where friends are given an unspoken and unquantifiable trust ranking and even that varies depending on the subject matter. Facebook can hardly mimic that level of complexity.
The end result is that many are now scrubbing their lists (much to the chagrin of those dumped unceremoniously) and have become more selective in allowing people in. That would surely lead to less traffic on the social network site. As for me, Facebook never was my cup of tea. Some old acquaintances are best left in the past, to be visited in memory or the pictures. For others, there's always email and telephone.