They don't know exactly who I am at all. That would take an IMEI number and a database that they don't have.
Completely untrue. When you sign in to Facebook on your device, they have access to your phone number (if you haven't already voluntarily given it to them) and device ID (not IMEI, but a unique identifier). They also get to have access to your contact list. All of your friends have also given them their contact lists. It isn't hard to correlate all those lists and numbers, combined with messaging histories and usage patterns, to know exactly who *everyone* is, even if you DON'T have a Facebook account.
That's the part that bothers me the most, is that even if I've never used their services, they still have a profile on me.
Zuckerberg was absolutely right when he called his users dumb fucks