To anyone who says, "helmets don't offer much protection anyway" who gives a shit? Don't you want to give yourself the best chance possible to save yourself in a gnarly crash? I've never heard about helmets contributing to head injuries.
Every year I retire my old helmet and just looking at it is all the reassurance I need, there are so much chips in it from hitting rocks, branches, exc.
Ohh yeah and everytime you have a really good crash where your helmet takes a really hard impact, you should replace it.
I started wearing one a few years ago and it has saved me from a lot of possible head injuries, it doesn't take a hard knock to break and unprotected head.