I won't speak for facebook but we REALLY DO spend a lot of time thinking about our privacy settings on foursquare, and we try very hard to balance a "as secure as possibly by default" vs a "as useful as possible by default" model while at the same time trying to make the options as easy to understand as possible for our users. If there's any specific way you think we might be able to improve I'd be very interested in hearing it.

-harryh, foursquare