I always think it's interesting to compare and contrast helmet use for different activities.

We're used to current recommendations to replace riding helmets after a few years or one good fall, and tons of kids play football in helmets that might be decades old, with more hits than you could ever count. And many of the helmets they use only meet standards that have barely changed for decades.

http://www.nytimes.com/2010/10/21/sp...elmets.html?hp