It might send web privacy campaigners scurrying for the terms and conditions, but what KLM is doing appears to be completely above-the-board and is actually a rather neat idea.
KLM takes note of passengers that check-in using FourSquare at various KLM locations around the world, such as departure lounges, baggage claim areas, ticket offices, etc.
Read the full story at http://www.tnooz.com/2010/11/23/news/klm-spies-on-social-media-to-give-passengers-a-nice-surprise/
