Or, Perhaps Not
At the risk of being ridiculed by the Kewl Kidz, I'll openly admit to having and using a Facebook profile. At this point, aside from immediate family, I think there might be ten or twelve people attached to it as "Friends," and that number seems to decline every month as I pare back to whoever genuinely brings some joy or insight to my day. (Another dozen or so are still listed as "Friends" but have been quietly blocked so that I don't see the drivel they post.)
I remember Vampires, and Farmville, and even pokes.
Family members who were avid, rabid Facebook users a couple of years back have tapered off in their activity. I don't know what's replaced it, but they use it a lot less than in the past, and they're really part of the target Facebook demographic. I think that on some level they too have grown weary of the bad UI, the incessant ads and unsolicited crap, and are also finding that Facebook just doesn't deliver enough value to wade through the mess that it has become.
What Facebook had in their favour, and which I'm sure they still think they have, is lock-in based on ubiquity: pretty much everyone you know is likely on Facebook, and it become the default place to reach them. The problem for Facebook is that if a significant part of that audience moves away it can snowball. Surely Zuckerberg is quaking at the possibility that someone, somewhere will invent the "new Facebook" that will manage to draw away their users.
Not only can it happen, it's pretty likely, especially since Facebook has one significant weakness: there's literally nothing that they do well, and most things they do poorly.
For me, it'll remain Twitter, which somehow is a lot more useful, a lot more entertaining, and seems to let me really carefully manage what gets presented to me in a way that Facebook either can't do, or can't do without digging through a bizarre and annoying menu system.