Helmets- ask 100 different people, get 100 different answers. Guess I'll throw my hat into the ring.
UV degredation. How may of you take your EPS liner out and let it sit in the sun? I can see the shell being compromised in time from UV exposure, but not the energy-absorbing liner. Interesting note.
I think the "5 Year Rule" is more advice, than a rule. I doubt that a well cared for and not used often helmet needs to be replaced every 5 years, but one that get's daily use in all types of weather may not hold up in 2. Everyone and every situation is different- Take it for what it's worth.
I have a gorgeous Shoei, Troy Lee, Kurtis Roberts Replica and I still use it, even though the "born on date" is 11/02. It's not my 'everyday' helmet, but it's still in the rotation.
Now, there is A LOT of validity to the technology of helmets improving over time, and I will happily retire my helmets that have a lot of life left in them, if there is a large leap in safety advancements. The Snell Rating was recently updated after a huge controversy over the old Snell Rating. I think it was Snell 2005 vs. Snell 2010 or something like that. The old rating required helmets to absorb a certain amount of energy that if that were to happen in a real-world-crash, the rider would likely not survive, so what's the point? The new rating is based on protecting your mellon, in a crash that you and I will have a reasonable shot at survival. This gives me thought on buying a new lid, based on that alone.
And, I love to buy new shit. That's just me, so I currently have about 8 or 9 helmets, both road and off-road that are in the garage- none are 'crash tested'. I let passengers and people use my old helmets, because even if they are not "fresh & new", I personally believe any helmet is better than no helmet.
Ride on and be safe brothers! (and sisters)