You've nailed it!
I'm 25, and was included in the first group of FB users back in 04. I've adjusted to the constant changes Facebook has thrown at me, and was a fairly engaged user until recently.
About a year ago I started noticing my FB wall/timeline/whatever was turning into a constant stream of baby images, ultrasound pics, wedding posts, buying that first house, and general crap that has nothing to do with my 'friends'. It was literally 60% posts about babies/children, and 40% about being engaged/married/in love. Not that I have an issue - I'm married too, but didn't feel the need to share every last detail of my relationship on there.
This whole parents effect, and all the over sharing associated with it, has caused me to leave Facebook for good, and I've a number of friends who have either done so or are thinking of doing the same. It's not that I am anti-Facebook, it's that Facebook has lost its usefulness for me.