how did someone find me on facebook when my profile's supposed to be private?

[weasel]

I have tried to make my facebook profile private. But, a person I know has tried to add me - we have no mutual friends, my name is really common, and she doesn't know my email address - how did she find me??

[?]

She could've looked at someone else's friends list that you're friends with (even if SHE's not friends with that person, some people's friends lists are public and anyone can look) and seen your profile.

Double check your account settings though... Click:
Account > Privacy Settings > View settings (under basic directory information) > and click the box next to "search for me on facebook" and make sure it's set to "friends only"... that way, people can't find you when they look up your name on facebook.