Remember when seeing an iPad on a bus, an airplane or the subway was a startling new experience? Now you might be startled not to see one.

Over the holidays, so many people bought tablets for each other (and, presumably, themselves), that U.S. tablet ownership nearly doubled among adults, to 19% in January from 10% a month earlier. The rate is growing quickly: In May 2010, shortly after the debut of the iPad, only about 3% of consumers over age 16 owned tablets, according to survey information from the Pew Internet & American Life Project.

The survey found a similar jump in e-reader ownership, as prices dropped below $100 for electronic book readers from Amazon and Barnes & Noble. Nearly 20% of U.S. adults now own an e-reader, up from 10% in November.

Tablet and e-reader adoption continues to grow quickly just as sales of traditional personal computers slow and even decline. In the U.S., PC sales last year had their worst year since 2001, dropping nearly 5% compared with 2010, according to research firm IDC. Analysts and PC industry executives regularly cite the increasing popularity of tablets when talking about the slowing growth of the PC businesses.

According to the survey, tablet adoption is now the highest among wealthier and more educated buyers. About 36% of those making more than $75,000 a year own a tablet computer, compared with about 16% of those making $30,000 to $50,000, although ownership rates in both groups appear to be growing quickly. The discrepancy is also substantial between college graduates, 31% of whom own tablets, and high school grads, at 15%.

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-- David Sarno

Photo: Boxes of Kindle e-readers sit at an Amazon.com distribution center. Credit: Chris Ratcliffe / Bloomberg.