I will always wear a helmet after an incident of crashing a motorcycle (800 CC, so a slightly different machine) resulted in me breaking the only bones in my life and KO'd me even though I was wearing a helmet. Had I not had that helmet on, I am quite certain that my head would have been moooosh on the pavement.

Traffic looks crazier here in Vietnam, but there is actually a system to it and once you understand it I believe the roads here are actually FAR safer than in Thailand. For one thing, the police actually do something over here like pull people over for infractions... in the near 16 years I spent living in Thailand I never saw anyone get pulled over.