I can see another problem. Security. People use their real names.
I'm securtiy concious when online and I never use my real name unless I have to.
I don't think people realise just how easy it is to commit ID fraud even with the barest of details, and people on facebook have only got to add you as a friend, look at your profile (I'm assuming they can when your "friends" with them) and even if you've only noted your DoB that coupled with your real name is often enough for your ID to be used for fraud as I understand it.
Of course I've signed up using an alias so unless it's someone who knows my alias people won't have a clue who I am unless they ask and I tell.
Guess I'm just paranoid like that.
I got really bored tonight and started looking up people I used to work with and currently work with, and it's quite easy to deduce that you are looking at the correct person if you look at their friends list and you know some of the people they might be friends with...
I should imagine facebook is a very useful tool for detective agencies.
Still haven't found my kent based family members, but then I know them only as uncle Dave and auntie Marie and I'm not bored enough to search through all the Daves and Maries.