From Publisher’s Weekly:

Total book sales fell 2.5% in 2011, to $27.2 billion…unit sales rose, however, up 3.4%, to 2.77 billion with the discrepancy due to higher sales of lower-priced e-books.

The increase in the sale of e-books was the major story in 2011.  In the trade segment, sales of e-books rose to $2.07 billion from $869 million as units increased 210% to 388 million. With the growth in e-book sales offsetting declines in print, total sales in the trade segment inched ahead, up 0.5%, to $13.97 billion last year. E-books accounted for 15% of all trade sales in 2011, up from 6% in 2010.

E-book vs Print:

In another sign that the industry is moving toward a hybrid market, fewer e-book buyers reported buying only digital titles this spring than a year ago. …[T]he percentage of e-book consumers who exclusively or mostly purchase e-books fell from nearly 70% in August 2011 to 60% in May 2012. Over the same period, the percentage of survey respondents who have no preference for either e-book or print formats, or who buy some genres in e-book format and others in print, rose from 25% percent to 34%.

I personally like both print and e-book. E because so many are often only available there (and there’s that instant gratification aspect) and print because I hate taking electronics to the beach!