Is this how it starts? Is this dot com ‘tall poppy’ syndrome or does the smoke point to a fire somewhere?
http://www.insidefacebook.com/2011/06/12/facebook-sees-big-traffic-drops-in-us-and-canada-as-it-nears-700-million-users-worldwide/

Looking back into history, this article showed the small decline in MySpace in 2006/07  http://www.socialnetworkingwatch.com/2008/01/december-comsco.html

The pace accelerated in 2008 as the competition hotted up –
http://www.guardian.co.uk/technology/2009/mar/29/myspace-facebook-bebo-twitter

The difference between the MySpace and FB is that it has almost become the defacto OS for the web – but in my view that only makes it bulletproof, not indestructible!

The recent changes in the developer rules in FB suggest that they have lost traction because they took away some of the flexibility and commercial freedom in the platform.

As your Nana and my Mum start to infiltrate the network who knows what brand(s) will rise up and challenge the the big F.  History will most likely repeat itself, because the digital space is constantly evolving and the same lack of control that most brands are struggling to come to terms with, also applies to FB, and as soon as we see something better we will inevitably move on…