I personally do not fly without one. I friend of mine died due to the fact that he was knocked out during the impact, thus unable to flee the ensuing fire.
Another pal has the remains of his bone dome, that he was wearing when his Pitts hit a ditch. The gouge across the top of it caused by the ignition key and various switches is sobering enough.
Even when I had to transit in a cherokee, I sat there helmet and chute!! But you have to admit that if they pulled you out of the wreckage, with a perfectly servicable chute and helmet sat in the luggage compartment. Then that would be even more ridiculous.