A couple months ago I was doing my semi-annual gear wash and when I took the foam knee armor out of my pants I found that it had started to split and fall apart (the pants are 6 years old). I'm sure it would have still provided some protect in a crash, but certainly not as good as it should have. Replacement pads were only about $25. I have Icon pants, but a pair of generic Joe Rocket CE pads from NewEnough fit just fine, and the soft armor can be trimmed to fit.
Anyway, for those of you who keep gear for a long time, check your armor from time to time.