Apple reported Tuesday afternoon that it sold 7.3 million iPads in the quarter ended December 25, up from 4.2 million in the previous quarter. Since the company released the tablet in April, it has sold approximately 13.8 million devices. And, according to a survey conducted by the Codex Group, iPad owners use their devices to read. A consumer survey conducted in early November found the 67% of iPad owners used the device to read and another 19% said they expected to begin reading with the iPad.

iPad owners are also buying e-books in growing numbers; 36% of books purchased by iPad owners in the month prior to the survey were e-books (compared to 46% for Kindle owners). But while Apple appears to be swamping the number of Kindles sold--Codex estimates that Amazon has sold 4.4 million Kindles--there is good news for Amazon. The Codex survey found that only 29.4% of e-books for the iPad were acquired through the iBookstore, while the Kindle store accounted for 40.3% of e-books acquired for use on the iPad.