Re: they know more than you know
I've always assumed the email address is the main thing it uses, as its probably the only thing given that is generally unique to one user and verifiably accurate in the basic sense that you can recieve the verification mail via that account.
So even a fake name account with a well used personal email address (as opposed to those junk addresses we use) would yield plenty of close contacts after FBs been through the users address books. If that email address appears in others personal address books often enough with your real name attached, I guess FB can also take a reasonable punt at the likelihood that is your name rather than the one you submitted.
Many of those contact books may/will contain other info you didn't submit like home address, workplace, photo, D.O.B., spouse, inside leg measurement etc. Again, if enough of those agree, I'd imagine it assigns a value for the probability that you are "X", based on the number of 'votes' for each piece of information. If some also have an alternative email for you, the same process can be applied to that, refining the probablility of who 'you' are further and perhaps netting other information.
All of that can then be checked further across other available sources; ad pimps databases, public records, website data etc etc, and anything new checked again from scratch. Face recognition would provide other potential matches by association too, if they have a starting point. By the end, assuming the original email address was pretty well used to contact actual aquaintances, I'd be surprised if they hadn't build up a pretty accurate picture of the accessible bits of your life, and have reasonable confidence that the core is correct. Obviously how much they can tease out is going to vary massively depending on how widely the address was used and how sociable you are as a whole. Not to mention how much horsepower they apply and storage they have, which would appear to be vast.
And all that potentially, from one email address and a few fake details. Caveat; there's a lot of guessing here.
But it gets even uglier when you think that you don't even need a profile for them to do this since your email addresses will already be available, without your permission, via the sucking dry of all those contact books; the so-called 'shadow profile' I've seen mentioned elsewhere, the idea of which I find extremely offensive since I really wouldn't piss on Zuckerberg if he was lit up like a roman candle.
FB makes the idea of maintaining somewhat discreet identities on the net extremely hard, because of its overarching view across so many data sources and because the discipline required to avoid cross contamination would just be too much effort. So one way or another, participate or not, Zucks sordid little enterprise gets to turn you into a cash cow for their profit, like it or not, either via selling your data, or via your participation in ad-clicking. Very wrong and very depressing.