Popular = how widely linked a site is (plus other related metrics), and yes, it does know.
Unless its extremely relevant, and there are no other equally relevant, but more widely linked or appropriate things, then no, it will not.
So I'm opted out of Facebook's functions by not being a member, but someone can still tag me in photos...a function of Facebook. Really...?
This is even dumber. You can untag yourself in photos if you're a member of Facebook. Why should you not be able to untag yourself if you aren't a member? Also why should someone be automatically opted into something they don't agree with? How is that censorship?