The mark is right above the Enter key. I've had my Air for a little over a week, and have taken great care of it. I honestly can't recall if this odd defect was there from day one or not. I certainly don't remember scratching it or applying any sort of significant pressure or action there. It's either a scratch or a crack. It's not a stain as it won't rub off. Opinions? If this is a legitimate defect, I may exchange my Air, especially since I have a "creaker" too. Think Apple will honor an exchange? I've run my fingers over it, and it doesn't really feel like a crack. I don't feel that sort of "break" in the material. Then again, it's such a small area. And i can only see it viewing it from the angle in the pictures. If I looked at it from the right side, the mark is nearly invisible, which may explain why I didn't notice it for a week until recently.