I have participated in the Winter Bash and can see that many users have profile icons with hats on it. I think I earned one hat, but can't see it on my profile. Am I missing something?
When you earned a hat, you'll be notified by the
Winter Bash notifier in the title bar:
And you'll find a hat count in your profile:
To wear a hat, click on the count and pick a hat to wear:
Alternatively, you can click on your profile picture (on your profile page) to switch hats. If you click the circled hat again, you'll remove it.