You stingy bastard. You know who you are: the guy who insists his gear is still fit for duty as it crumbles into dust. Everyone is guilty of it, but we all need to take a deep breath and realistically assess the state of our gear.
Black Diamond's quality control lab hooks us up with pointers on how gear degrades, what to look for and what to do about it. This edition focuses on slings and quickdraws, but there's plenty more on their site so dig around.
The bottom line: BD claims two main factors wear out slings and draw, and those are abrasion and ultraviolet light. One interesting finding is that both nylon and Dynex degrade similarly from UV, and most of that 16% loss in strength happens in the first ten weeks. So don't think it's even over time.
Their next gear lab will focus on biners, so stay tuned.