Re: Users you've never heard of saying hi and friend requesting you.
Here and elsewhere (so basically everywhere except real life, because real life doesn't have lists) I'm rather picky. I only accept requests from people I at least somewhat know (and like), and tend not to request from others unless I have more than the one obvious reason.
So as you can probably tell, I don't accept friend requests from random people I don't know. I will however politely decline by telling them why.