From the press release.  I should note that Book Industry Study Group surveys are pretty rigorous in their methedology:

E-book consumers’ preference for tablets is accelerating rapidly as dedicated e-readers drop in popularity, according to the Book Industry Study Group (BISG)’s closely watched survey. The second installment in Volume Three of the study shows that, over the course of just six months, consumers’ ‘first choice’ preference for dedicated e-readers such as those from Amazon and Barnes & Noble declined from 72 percent to 58 percent. Tablet devices are now the most preferred reading device for more than 24 percent of e-book buyers, up from less than 13 percent in August 2011. Further, the increase in tablet preference was not primarily for Apple’s iPad (which rose by just over one percent), but for non-Apple tablets — overwhelmingly from Amazon and Barnes & Noble. These non-Apple devices increased from five percent to 14 percent over the same period.

‘The movement from dedicated e-readers to multi-function tablet devices is an important one for publishers to understand, as it allows them to deliver a richer, more interactive e-book experience,’ said Angela Bole, BISG’s Deputy Executive Director. ‘One of the strengths of this study is that it can plot such evolution, preparing publishers for what e-book readers want and expect from them next.’

The study, powered by Bowker Market Research, points to a buoyant book market. Nearly 30 percent of respondents in the February 2012 survey reported an increase in dollars spent on books in all formats since they began acquiring e-books, while nearly 50 percent reported an overall increase in the volume of titles purchased in any format. The numbers are even rosier for the e-book market: more than 62 percent of respondents reported an increase in dollars spent on e-books, and more than 72 percent said they have increased the volume of e-titles they are buying. Some publishers are reporting that even when overall revenue has declined, profitability — particularly for e-books — has increased.

In addition to ‘Power Buyers’ (those who acquire e-books at least weekly), this report looks at the behavior of ‘Casual Buyers,’ who purchase one or two books a month. The study reveals that this second generation of e-book and e-reader adopters is catching up with Power Buyers in a number of ways. More than 27 percent of Casual Buyers now exclusively purchase e-books rather than print, compared to 30 percent of Power Buyers. Further, Casual Buyers are only slightly more likely to play games (37 percent vs. 35 percent) or watch video content (23 percent vs. 21 percent) on their devices. However, Casual Buyers lag significantly behind Power Buyers on the uptake of multi-function devices. Only half of Casual Buyers use a tablet regularly, compared to 83 percent of Power Buyers. “