I put Nokon cables on my bike in March and was initially pretty happy with them, but I've had problems twice now with the shifter sucking the plastic lining out of the cable and into the shifter, clogging everything up. It was happening a few weeks ago, but I used some spare cable lining from the kit to fix it. Then at Wildflower I lost my 4 lowest gears in the back, which was a real problem (though losing the highest - climbing - gears would have been much much worse!).
I've been so frustrated that the problem came back that I haven't ridden in two weeks (I've not had time until today to really try to fix it, either)
I think I have it fixed again, but I suspect the problem will come back. There is an inherent flaw in the design where the inner cable lining can slide inside of the outer ferrules. If the metal cable itself has any amount of friction on the lining (and of course there's no way to eliminate friction completely) it can pull the liner right out. If it pulls it out just enough that the shifter can grab it, it's game over and you're going to get a shift lever full of plastic.
I've tried searching to see if anyone else has had this sort of problem and found nothing. Perhaps I'm an isolated case or perhaps I've installed it wrong. I really like the concept of the nokon cables -- they look sick and allow me to run much tighter routing than traditional cables, and they definitely improve braking -- but if this problem comes back at all I'm probably going to trash em and go back to traditional cables. I am actually tempted, too, to switch to SRAM or Campy because I feel like this is partly Shimano's fault as well.