Yeah the price is steep for just a thumbstick cover but they are apparently really good.

Not sure where you are located but in the UK I contacted Sony and returned both of my controllers which were suffering wear. These were replaced/repaired by Sony and returned free of charge.

(turn around time was i think 2 maybe 3 weeks)

Well I am in Japan so i might bring the dualshock to the door the the Sony headquarters and carry out a silent protest.

I've been using a pair on an XB360 controller and another pair on a DS3 controller for years. At $10 a pair, that's the most anyone will probably pay for something that costs maybe $.50 at most to produce (on bubble card), but... it's hard to argue with what has obviously worked for me. 

I've had good luck with the silicone "caps" that stretch over the thumbsticks on the PSVita, so I wouldn't mind using a pair of those with a concave design (my preference) on a DS4 instead of the FPS Freek grips. 

That's already fixed since at least code version 13............, that was my replacement DS4, was told so by the official Sony service employee, and yeah, they feel different. Less traction than the original DS4 though :-/

I've also put some of the grip it thumbstick covers on, within the first week or the PS4 release last year.

Quote from a GAF member:

"Easily the best controller Sony has DESIGNED.

But the worst controller they have MADE. "

I'm going to agree with that.

While my thumbsticks haven't worn through the rubber coating as I've seen happen (I tend to only play with clean hands, which can't hurt), they definitely wear down faster than the DS3.

But a larger gripe I have with QC on the DS4 is that my L1 shoulder button sticks (no, it's not dirty; see above statement) due to tolerance or molding issues. I loosened the screw behind the L2 button, but it seems to be more of an issue of the entire housing being torqued down unevenly or warped. Every time I think I have the issue fixed by loosening the screws, cleaning the plastic abrasion dust out of the button well, etc. the issue comes back while I'm playing. 

I'll buy another one when they finally go on sale, but it has been an annoying downside to an otherwise brilliantly designed controller. 

For further pictures and issues:
http://www.neogaf.com/forum/showthread.php?t=877253

I wonder whats up with the QC on the controllers.. Lots of people with PS4s saying DS4's seem to be suffering from the same problems; after a while.

OP: I'd contact Sony and see if they can replace it with a new one.