There are literally hundreds of ways to narrow people down. With some simple sleuthing and a little patience, people can find you based on even the smallest detail.
Seeing where you've been...
Here's where Graph Search starts to get really freakin' creepy. You can use it to find out what parties someone's been to, or locations they've checked into. All you need to do is type "places X person has been in the past X months/years" or "events X person has attended."
... and what your interests are
Unless you've Fort Knoxed your privacy settings, anyone can easily find out the bands, movies, books, websites, people, or groups you like. All it takes is your name and a few keywords in the search bar, i.e. "pages liked by X person."