KLM have been experimenting with social media to enhance customer loyalty for several years now. Last year over the holidays they intercepted random passengers waiting for their flight who had tweeted about flying KLM and handed them a small gift. The experiment was a hit.
This year they are helping their travellers have an even more memorable holiday by offering up a service that turns anyones pictures and videos into a movie. The service is delivered in the form of an app. It is super simple to use and very fun.
I really like this idea because it requires so little involvement from the user (unless he/she wants) but the reward is so high and the ability for the output to be shared and turned viral within the users social graph is high. Absolutely brilliant.