I think there should only be a half dozen or so hats awarded for "normal use".
- most users should be able to get all hats, so everyone can join in the fun - it's about participation, not a competition
- de-gamify the event. Having obscure or secret hats is counter productive, elitist and IMHO not in the spirit of the many "family events" that are happening at this time of year
- lose the leader board! Why is there even a leader board? If we don't want gamification of hats, why do we have a leader board?
- lose the hat count on the user profile page too! Don't score what shouldn't be scored. Maybe have a row of a few hats to chose from, not yet awarded hats are greyed out. Click on the one you want to wear. Simple
Suggested examples of events that unlock hats:
- an answer is accepted
- a comment gets 5 votes
- use the site 5 days in a row
- a question gets 5 votes
- an answer gets 5 votes
And maybe one or two slightly tougher ones, but nothing too crazy:
- hit rep cap
- review one of each kind