I never used to wear helmets when cycling as a child and teenager. Now that I've grown up, I do.

Here are some cycling injury findings.

http://www.preventable.ca/articles/7...-have-crashed-

Coles' notes for the lazy.
" ...
Half of all cycling injuries and deaths happen in the summer.

The majority of bicycle injuries do not involve motor vehicles. Most are falls, collisions with stationary objects, and collisions with other bikes or pedestrians resulting from the bicyclist losing control.

Helmets can reduce the risk of head injury by 88 per cent if worn appropriately while cycling.

Those who survive unprotected bicycling brain injuries may suffer epilepsy, intellectual and memory impairment and personality changes.
"

Some stats from Alberta Health regarding head injuries for cyclists.
http://www.stop-injury.ca/documents/...adInjuries.pdf

I wear not because of the law, I wear because my head is worth it.