Just to demonstrate how things change, my kids (college and high school aged) are cooling rapidly on Facebook.
I'm 21 and rapidly cooling on Facebook. I only use it to create photo albums so friends in the USA can see what I'm up to. You're right that Facebook is increasingly powered by ads, but it's also commoditizing every element of one's personal description.
What I mean is, you used to join groups describing you, like "I Survived Mr Ormiston's Physics Class" or "The Beethoven Appreciation Society," and you used to have boxes where you could write all your favorite movies/TV/whatever. Now, that's changed: instead, you browse through official pages operated by the TV show, or movie studio, or corporation, and hit "Like" when you like one. Only when I "like" something is it clear to my friends.
So for example, a year ago all my friends could go to my Info and read a list of my ten favorite books. Now what they see is a list of three or four books which have official pages - ie, you click on the book, you get an official summary of its contents, a cover photo, and an ISBN number so you can go to Amazon and buy it.
I've just noticed while writing this post that I used to have an "interests" box that said "reading, writing, walking, baking desserts, finding new Turkish restaurants, Washington Nationals baseball" or something like that, but the "interests" box has been changed without my permission to say "The Economist, The New York Times, Petrucci Music Library, Roger Ebert"! When I decided to change it back, I typed in "Wri" and was offered a choice between "Writing", "Reading & Writing," or "Writer." So you can't just make up your own unique interests anymore.
