Just noticed it today but it appears they've been there for a while since they have blackened. These are hairline on the hinge portion of the cover (screen), all the way from one side to the next. I have Apple Care but won't bother asking for repair,it doesn't affect the MB's performance anyhow. Any one else seen these or heard of reports about these?
I had the keyboard replaced a few months ago because of the cracks on the inside but these new cracks are on the outside
Apple has been fixing cracked cases (bottom, anyway) for a while now - whether the machine is still under warranty or not. I'd get it fixed if I were you - it could get a lot worse. No harm in trying. You'll probably have to take it into the Apple store.