KLM Surprise is a very innovative use of Foursquare.
KLM has set up a Foursquare account, and is asking people to add them as friends. Travellers who do, and then check into KLM locations like airport lounges are then studied (for example their recent tweets) and some are rewarded with unusual and thoughtful gifts based on what KLM can work out about them.
The Next Web has more details:
"The KLM team has surprised travellers with champage, notebooks, a watch, and traditional Dutch foods. One passenger, Willem van Hommel, was going to miss one of his soccer team’s most important matches of the year due to his trip to New York. KLM surprised him with a Lonely Planet guide to New York with all the best soccer bars in the city marked out for him. Another traveller, Tobias Hootsen, was surprised with a package to remind him of home during his long stay abroad."