My iBook has quite the same problem, but it is limited to the region on the battery. The saddest thing in my case is that these marks appeared after I went to my local Mac dealer to ask them to repair a completely different problem. My initial problem was that when I opened my iBook, the cover made big noise like it was going to crack. It was like this since I bought it, but at first I thought it was because it was new, and I waited, hoping to see the noise disappear. But it didn't and it was even louder. So, after bringing it to the store where i bought it, I had to wait 3 weeks to learn that my case was classified as an aesthetic problem, and that they couldn't do anything. I had to call Apple, because only them could repair the noise problem. Then I talk to Apple technicians, went back to the store to get my portable, and saw the marks under the plastic. I was really shocked since they took three weeks to do any single thing, and that they even damaged the iBook I consign to them. They denied the responsibility for the damages in the plastic, and told me Apple would do the repair. Of course, when I talk again to Apple's technicians, they couldn't guarantee that the repair would be done, since it might not be covered... I hope the marks will not extend to other area than the battery, and the only thing I hope for is that Apple will send my iBook as it should be, or that the store will offer me a new battery with no damages on the plastic.
