20% of U.S. Population Has Never Used Email

Ezratrumpet writes "A recent PC World article notes that 20 percent of the U.S. population has never sent an email. Does this number over- or underestimate the actual number of people who know nothing of email? What are the implications of this statistic to our society? Or are these people just Luddites who mourned the demise of the telegraph and have also never used a telephone?"