It's true, the screens used on the latest Apple iPod Touch and iPhone are difficult to scratch because they use glass instead of plastic. We take glass for granted, but it is an extremely hard material that resists wear and tear from common abrasions. Another benefit of glass is that it is one of the most transparent substances on earth and offers superior visibility for applications such as telescope lenses and television screens.

Glass isn't perfect, however. Compared to plastic, glass is much heavier and more brittle. So while dropping the iPod Touch on the ground might not scratch the screen, it could shatter it.

Still, with Apple leading the charge, I suspect we'll be seeing more glass screens on MP3 players and portable video players. We've already heard that the new line of Zune players from Microsoft will use glass screens instead of plastic.