As you can see in the video below, as the iPad is rotated into a portrait orientation, screen visibility is completely lost. In comparison, the iPhone’s screen is polarized at a 45-degree angle making the device usable in the most common orientations – portrait and landscape.
This effect is not limited to iPads or Apple products; all LCD screens are affected to some degree or another. While some have an extinction point, like the iPad, others only have a color shift. The most common practice among manufactures is to orientate the polarization at a 45-degree angle, as seen on the iPhone, to minimize the impact.
While this probably isn’t the most common issue, and certainly not a deal breaker for most users, it is strange that after 3 releases of the iPad, Apple still hasn’t adjusted the polarization angle, especially considering that people today are using their tablets everywhere and in a wide variety of application.