I think that it's the surface of the pad...changed to make it feel more like paper or something but it wears the nibs quickly. Last I heard, which was a while back, was that Wacom was going to have another surface you could stick on. Seen some folks tape plastic sheets and other things across them. Me? I can spare $15 for nibs every year to keep my Intuos4 looking all black and stylish...with no duct tape and chewing gum holding something to the front of it. My old Intuos(no number) was great though...I don't think I ever changed a nib on it.
M