Fun is something everyone loves and it can make any experience better, but few people really understand it. Fortunately, Raph Koster has turned fun into a science and he breaks it down in this keynote from the O'Reilly Emerging Technology Conference. He gives a list of ways in which an activity can be made more fun, with examples from social media and ecommerce.

Fun comes from learning and mastering new experiences. Just as any game is composed of smaller sub-games that need to be mastered, so can any activity be broken up into sub-activities, all of which can be made more fun. Some of the elements of fun are that how you complete an activity should matter, it should be hard enough that there's a chance of failure, that should be able to get better with practice, and that context should be provided and should matter for every action.

The example that Koster uses for all of these examples is shopping on Amazon (a straightforward, consistent experience that's not very fun) vs. shopping on eBay. On eBay, you can learn tricks that make it easier to succeed, there is risk and possibility of failure, and there are different ways to approach the same action. As a result of these and other fun features, people become much more involved in an eBay purchase and have more fun doing it.