In this article from Publisher’s Weekly, the growth of ebook sales is compared to print versions.
Ebook growth continues to be enormous just like it has in past years. But don’t let one important statistic slip away in the comparison. The 5% growth quoted for print exceeds the industry wide growth rate seen in recent years.
Also remember that these are Amazon’s statistics only. Be aware of what’s going on in the larger arena to get a real picture of what these numbers mean.