I usually wear one when biking in Manhattan, but I rode Citibike today and went helmetless.
This is probably statistically whack, but I "feel" safer riding Citibike without the helmet, mostly because I can go a lot faster on my road bike.
And some evangelizing against helmet laws: http://www.copenhagenize.com/2008/08/helmets-or-health.html
I usually wear one when biking in Manhattan, but I rode Citibike today and went helmetless.
This is probably statistically whack, but I "feel" safer riding Citibike without the helmet, mostly because I can go a lot faster on my road bike.