Has anyone using the newer Wacom tablets ever had a problem with the nibs? There's a lot of stuff on the net with people complaining that the nibs wear down way too fast. I'd find it very odd, especially considering I've had my Wacom Graphire4 for years, and although the rubber on the pen grip has long since dissolved, the nib is still pretty much the same as it was when I got it (or at least it feels like that). This may be because of the plastic covering I have on the tablet (which came with it, I might add).