The iPad 3 is now in manufacturing and the inevitable leaks keep coming out from part manufacturers, including images of its double-resolution Retina-ish display and its brains. Now it's the turn of the outer aluminum shell, which reveals some interesting details.
First, it's a bit thicker than the iPad 2, but only about 1mm (0.039 inches), which will not be noticeable. The bezel at the edge of the shell is thinner than the iPad 2. The shell also has a smoother, longer tapering. MicGadget claims that the Wi-Fi and 3G model will be 0.5mm thicker than the Wi-Fi only one.
Finally, the case seems to have a larger opening for the rear camera, which may indicate a larger lens and sensor.