Plasma TVs rely on a thin layer of gas (which gets ionized and eventually turns into the picture you see). If you think back to your chemistry classes in high school and college, you might start remembering. You might also recall concepts like the ideal gas law (PV = nRT), which basically says that (all else being equal) the volume of a gas is inversely related to its pressure. This is a nice way of saying that if the atmospheric pressure goes down (as it does at high elevations), a gas expands.

As some folks living in high-altitude cities have discovered, this expanding gas can cause the glass screen in a plasma to bow outward and potentially vibrate and make an annoying noise. If you live some place high (say a mile above sea level or higher), check the manufacturer's specs before buying a plasma set. In response to this, manufacturers have begun to make specific design changes in reaction to this situation and have begun selling plasmas that won't get altitude sickness.

The bottom line is that you might hear stories about plasmas having issues at higher elevations. The altitude or gas issues plasmas have had in the early days have been effectively solved with the latest models.