Facebook is fab, but it works in mysterious ways and it is highly unlikely any of us non-techs will ever get to the bottom of exactly how they make the friend suggestions or how they mine your information in other numerous ways.... god knows I've spent long enough looking for reliable technical explanations on the internet with very little success.
I opened a Facebook account without downloading ANY of my email address book contacts. Not one. I have ONE friend only on the account, my niece. And yet, Facebook still sends me friends suggestions of people who I DO know, but could NOT have been gleaned from any email info I knowingly provided to Facebook. Today, as an experiment, I visited my niece's profile from my Facebook page and clicked through to some of her friends' profiles. Hey presto, ten minutes later I check my account and suddenly scores of teens and twenty-somethings from my niece's friend list ( and maybe even from her friends' friends lists) are popping up in my friend suggestions list. So I can tell you with certainty that it is NOT the case that friends suggestions are unconnected to viewing other people's profiles, as some posters here have suggested.
Whatever you think about Facebook, the important thing is just to realise they CAN and DO mine your data and use your personal profile in unfathomable ways!! So don't be naive and either consciously take the decision to throw caution to the wind, or else follow the golden rule if you want to stay on the safe side - which is that you don't put anything on there, ever, that you wouldn't be happy for ANYONE to see.... because they probably WILL be able see it, sometime, somewhere in the future, if they look hard enough.....
PS, although Facebook is clearly mining information from profile views somehow, the one thing I'm fairly confident of is that other people do not know you have viewed their profile, so peek away!! :-)