Black stripe up

When putting a MacBook in a bag, always put it black stripe up. The fans (and only ventilation) are situated in the hinge behind the black stripe. If your machine is hot, and you put black stripe down you are either forcing all the heat through the machine (if the fans have turned off) or are essentially blowing hot air over your screen, which can cause shadows on the lower edge of the screen.

If you put your computer in the bag black stripe up, the heat can naturally escape without coming in contact with components, thus reducing the wear and tear on your Mac.

Now if only Apple would put a sleep indicator on the back side…