We participated in 2013 and I think a lot of users had fun with it (especially e-sushi who seemed to find the most hidden hats if I remember right).
Winter Bash is an annual event that can run on any Stack Exchange site that chooses to participate. Users earn “hats” for their gravatars by completing certain tasks (analogous to badges). Certain actions trigger the user receiving a hat, which their gravatar can “wear”. We track everyone’s progress earning hats in a leaderboard that looks something like this:
Winter Bash 2014 will again be available to all sites that choose to participate. We’re redesigning all the hats and adding some extra features to keep things fresh and exciting.
This event will run from 15 December 2014 to 4 January 2015. Users will be able to see their entire hat collection on winterbash2014.stackexchange.com. That site will also have a landing page, explaining the rules and other details of the event.
Individual users who don’t want to participate, don’t want to see hats, and/or are generally anti-hat will have an “I hate hats” option available. And just like last time, at the end of the event, all hats will go back into storage.
The only visual change to the Stack Exchange sites themselves will be the presence of the hats and the “I hate hats” button in the footer.