Welcome to Cake, kimmycake. 🙂 One of the productivity things I feel about Facebook is I'll see birthday greetings on my timeline from people I've become Facebook friends with over the years, maybe because they're photographers and I admire the photos they post.
It's nice, I appreciate the sentiment. Wait, do I know them? Hmmm, maybe I'm supposed to. Maybe they're a customer or I met them somewhere? Better say happy birthday back on their timeline when it rolls around. Wait, would that make them feel obligated to reciprocate every year? And that's how I got on a happy birthday wishing spree for awhile before it got unmanageable.
I don't blame Facebook for it or my friends, it just seems like an awkward unintended consequence.