My opinion ...

The efficacy of cycling helmets is probably wildly overstated to the public. Will it save your life? Almost certainly not. Might it prevent a boo-boo? Certainly could. Note that there are some reasons to believe that helmets could cause injuries too. Long story short, cycling helmets are designed for the types of injuries little kids suffer. If my memory is correct, they are designed for a standing two-meter fall onto a hard surface.

If a 100+ page thread isn't your thing, here is a good summary of the research.

http://www.cyclehelmets.org/