I just attended a very informative CAN Bike seminar and learned some very interesting things about bike helmets (and other stuff too!).
First, in Ontario they are mandatory for anyone under 16 but really, if you are riding on the road, WEAR ONE. Be a good example for your children and other cyclists.
Second, they expire after 2 years or 1 crash, whichever comes first.... hopefully it expires.
Perhaps you are wondering why they expire...the material that they use to create most helmets hardens as it ages eventually rendering the helmet ineffective after a few years. I was wearing a 10 year old helmet (there is a manufacturer sticker inside the helmet with the date)and I didn't even know! This evening, I will be proudly sporting my new Red/White LG helmet to match my gear! Woo Hoo!
Third, there is not alot of difference between a $50 helmet and a $300 helmet. Most of the comfort comes from the air vents to keep your head cool.
Lastly, proper fit technique...helmet should be two fingers above your eyebrows, the straps should meet right under your earlobes and the one or two fingers below your chin when buckled. Use the back tensioner to tighten the helmet so that when grabbed and wiggled it shakes your whole head and not just the helmet.
And...I'm not sure where you all shop but I found some fantastic deals on bikenashbar and got my regular priced $110 helmet for $49. They have lots of styles, colours and price ranges to suit every budget.
So no excuses people, if you are going to ride get yourself a good brain bucket and WEAR IT.
Let me know what you wear...