Ownership of eBook readers doubled in the US in the 6 months to May 2011

"The share of adults in the United States who own an e-book reader doubled to 12% in May, 2011  from 6% in November 2010.  E-readers, such as a Kindle or Nook, are portable devices designed to allow readers to download and read books and periodicals.  This is the first time since the Pew Internet Project began measuring e-reader use in April 2009 that ownership of this device has reached double digits among U.S. adults.
Tablet computers—portable devices similar to e-readers but designed for more interactive web functions—have not seen the same level of growth in recent months.  In May 2011, 8% of adults report owning a tablet computer such as an iPad, Samsung Galaxy or Motorola Xoom.  This is roughly the same percentage of adults who reported owning this kind of device in January 2011 (7%), and represents just a 3 percentage-point increase in ownership since November 2010.  Prior to that, tablet ownership had been climbing relatively quickly."

Source:  Report by the Pew Internet & American Life Project, 27th June 2011