I got my 360 around launch day, and although that has since suffered a RROD and was replaced last year, I still have and use the same controller from my original deck.
When I brought a new up 360 controller earlier this week, I immediately noticed this new controller felt a bit, different … Check it out:
n00b 360 Controller
VS
Veteran 360 Controller
Yep after years of play, the nubs on the left thumbsticks on the old controller have actually been worn down… 
the right nub has more or less completely gone. Master Chief himself would be proud of this battle scarred veteran.
I’m sure some of the ones in QA are waaaay worse
…actually I know they are…most have no rubber left at all, just smooth plastic!
One of mine has gone really weird, if I leave it in the sun all day there is an oily film on top of the thumbsticks…pretty gross…it’s been demoted to controller 4
I’ve seen nipples that have suffered a similar fate.