The FOAF search engine plink has been shut down because of people's complaints. That is indeed a challenge with social software: some relatives/friends/colleagues does not want to show up on some webpage while using google. Orient Lodge postes about it:

Plink “has shut down. For now.” Why? Julian Bond writes at Ecademy, “The interesting thing here is that there are approximately 15 Million structured data files out there on the web in XML of which FOAF is just one type. And the search engines currently do nothing with it. And when a programmer does try to do something, they get abuse from people who don't realize they didn't have any privacy anyway.”

Dom Ramsey writes at rdfweb-dev, “It was fun to do, but I'm now getting way too many complaints from people who have appeared without permission in other people's FOAF files and have found themselves via Google.

Trying to explain FOAF to these people generally doesn't work, and more often than not, they're too irate to care. So the easiest thing for me to do is just take the site down.“