if the guy who wrote an app that lets you carve Halloween pumpkins has over 100k daily active users, then seasonal facebook apps are a reality, and a force to reckon-with.
seasonal social apps
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http://wiki.developers.facebook.com/index.php/Data_Store_API_documentation
http://www.techcrunch.com/2007/10/03/amazon-takes-another-step-towards-the-web-os-with-dynamo/