This is true in my family. I'm reading books in the iBooks and Kindle apps, my wife reads samples in iBooks, and my mother has been reading voraciously in iBooks.
According to a survey of UK iPad owners put forth by Cooper Murphy Webb, people who own iPads are now using them as their preferred device for reading newspapers, magazines and books. Of the 1,034 iPad owners polled via telephone between July 28th and August 10th, 43% use the iPad for more than 10 hours per week, with most of those usage hours taking place in home.
Giving ammunition to the “iPad Will Save Reading” camp, 31% of iPad users prefer their iPad to their laptop, mobile phone, e-reader and print media for reading newspapers and magazines, perhaps due to the innovative presentation of news put forward by aggregator iPad apps like Flipboard and Pulse.
And moreover 41% of iPad owners prefer the iPad for reading books, which bodes well for iPad apps like iBooks, Kindle for iPad, and Barnes and Noble.