Jacqui Cheng on Facebook using users in ads:

Still, there are ways in which the system could be improved, especially for those concerned about their privacy being respected. The most obvious is that users are not notified that their posts are being used in ads, and cannot block their posts from becoming ads unless they change their privacy settings to make the posts private. That’s one thing Facebook has going for it this time around, though—the company will respect all privacy settings so that only the people you’ve already authorized to see your posts will see ads with you in them.

Ok so here is what is happening: say you check into Starbucks a couple of times. Facebook may use that data and your profile picture displaying it to other users that would normally be allowed to access this data already. Except that instead of seeing it in a normal way it is shown as an ad for Starbucks.

This all seems rather harmless until you think about this: what happens when you check in somewhere that you would never want to come back to?

Checking in somewhere is in no way an endorsement of that place – yet Facebook is using it as if you are endorsing it. Perhaps you are only checking into Starbucks because that is the only place you could find.

Not only is this a privacy concern, but it could really piss off your friends if they think you are endorsing a particular place.