Hahaha, I've seen a bunch of people riding like that - I wonder if they plan to dip their head into it upon an accident...

I replaced a helmet last year due to some damage received while my bike was taken from my back yard and later recovered (the helmet was locked into the u-lock, too).

I can see the foam being degraded by sweat/UV - that I buy... Unless it's been in an accident, I'd be wary of this 6-month talk. I've only had my current helmet for about 10 months but I sweat like a hog, I'm not even close to considering replacing it.

The way mine is going, the straps are going to go before the foam - sweat seems to be making the tell-tale salt-markings on them, I'm concerned they'll rot through eventually.