Last year, I collected 12 hats in StackOverflow's Winter Bash.

Winter bash Stack Overflow 2014

This year, I have 15 hats: I could get some more, for instance by deleting one of my own answers, or by doing complicated things such as voting to close a question, edit the question, and then reopen the question, but I'm not that obsessed by those hats ;-) I collect hats because it's fun ;-)