If someone needs to know who that actor is, I'll be asked. I might have never seen them in anything, but if I can't tell you their name (I am not that great with names... celeb names tend to be a bit easier though), I can tell you what other shows/movies they've been in or something random about them at least.
My brain will also select things about people that are similar to other people... the shape or the way they move, specifically. My brain often makes me think of Tyra Banks if I see Mandy Moore talking, for example, because their mouths are a similar shape and they move them in a similar fashion when they speak. So whenever I see one of them, my brains tries to remind me of the other. It can be useful when I see someone from afar though... just the way they walk (even when I'm not wearing my glasses, so can't see any features) can have me picking up on who they are.
Mostly, it's a useless skill though.
So what's yours?