That figure, based on 60,000 respondents to the survey, is twice the number the research firm found in its report a year ago. Forrester's figures are not that far off from a survey released in October by Pew Research, which found that 22 percent of adults in the U.S. own tablets.

E-Readers Dropping

About a quarter of all adults ages 24 to 46 own a tablet, the Forrester report said, and it projected that the current total of 34 million tablets in the U.S. will soar to 113 million by the end of 2016. Meanwhile, as full-featured tablets become more affordable, powerful and diverse, e-readers are plummeting.

In a report published Thursday, market research firm eMarketer found that worldwide shipments of e-readers would drop 36 percent this year, from 23.2 million units last year to 14.9 million units. Forrester projected that e-readers will sell only 7.5 million units next year, dropping to 5.3 million in 2014.

Forrester analyst Sarah Rotman Epps told The New York Times that it appeared e-readers "were a device for a particular moment in time" that are being replaced "more rapidly than we or anyone else thought."

At one time, Current Analysis' Avi Greengart could have been surprised at the speed with which tablets have taken over. When asked if he was surprised that they've already reached one-fifth of the U.S. adult population, he said he "would have been, maybe three years ago." Once the iPad emerged, he said, it became "quite clear that it was almost instantaneously going mainstream."

'Simplified Computing Experience'

The appeal of a tablet, Greengart said, includes the "simplified computing experience" it offers, as well as the availability of a powerful computing device that, in many cases, is less expensive than a laptop . He added that the "center of gravity" of personal computing has shifted toward this simplified experience, some of which is content consumption and some is "smaller, shorter, lighter" content creation.

Greengart said tablets were providing hundreds of thousands of what he called "bespoke experiences," such as an interactive view of the stars. "We call them apps ," he said, "but they're really experiences," and thus move personal computing away from the task-oriented functions that have been common with laptops and desktops.

If tablet ownership doubled in the last year, how long can it continue at this growth rate? Greengart said he expected a robust growth rate to continue for a while, even to the point of saturation among U.S. households.

Forrester also noted what could be the change wave right behind tablets -- connected TVs. The report said that 43 percent of Americans with Net access went online in their living rooms with their TV sets in the last year -- either in the most popular way, via game consoles, or through connections in TVs, DVD players or set-top boxes.

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