Subscribing to Madness

I wonder why Facebook is constantly suggesting I subscribe to Jessica Alba. (And what, exactly, does it mean, if I "subscribe to Jessica Alba"? Will she show up in my mailbox? She'd be really crowded in there. Or perhaps I simply have to agree with her on everything. I kind of doubt that.)

Is it because 4 of my friends subscribe to her? I'm pretty sure I have more friends subscribing to other people.

Is this a paid advertisement? It doesn't say so as the actual ads do.

Is it just because Facebook likes her? Is she a personal friend of Mark Z? Or the fantasy girl of some programmer at Facebook?

Has their ad cross-reference generator, which decides what they think I'm interested in, decided I am interested in her? If so, why? I liked her in the Fantastic Four movies but it's not like I'm enamored, or stalking her.

Facebook, what are you thinking?

Oh, wait. I never do know that, do I?