Yep, I've seen that one, and wished I could slap the person who posted it.
I guess I'm one of those "PC savvy" folks. I don't inherently trust or assume anything about any software. I check out every menu and every option, and make sure I know what it's all about. I found Contacts a while back and noted that it had phone numbers. Yay. But it only had a dozen or so, because most of my friends are too paranoid (or smart) to add phone numbers to their profiles. But as it happens, I've used this feature twice to call people when I didn't have their phone numbers.
What makes me really facepalm are the warnings about how Facebook has all of your information and it's "out there" for everyone to see. Facebook doesn't have anything that wasn't entered by the user, and it's only visible to those to whom the user makes it visible. Still, Facebook is just a database and can be hacked, therefore I always advise people against entering personal info, even if they're reasonably intelligent and understand security settings.