"It's unintuitive to think that games where you actually do not ever directly interact with another person could have a community, but what social games do is generate an asynchronous cloud of persistent community formed by the constant exchange of gifts, tools, and requests sent by other players. It's generosity-driven, but transactional - if I send you a gift, I'm feeling happy because I helped you out (especially if I'm responding to a request you've put out), but I'm also hoping you'll send me something back. And the more I send and receive, the more I plant, the more I return every day (or more than once a day) - the more hardcore my play becomes. Watch a hardcore FarmVille player. They move fluidly and attentively around the tiniest change in mechanics, and play not for some whimsical dollhouse experience but for tight, fast, controlled optimizations, seeking the fastest path to a clear goal, and putting in as much time as it takes to get there.
"In GoPets we knew that generous players were sticky players - meaning that we kept them for a long time - and so we incentivized generosity in our player base. But because our generosity levers were "manual" - players had the ability to send gifts, and socially benefited from doing so, but there were no specific mechanical achievement or requirement structures around them - our community was more genuinely social and less frenetic than its social game antecedents. The basic concept held true: Encourage players to exchange valuable items and they'll create an atmosphere of positive assistance that will in turn bring them to associate the game with generosity and positive feelings."-Game designer and writer Erin Hoffman explains how the gifting system is key to the appeal of many social games.