According to an industry research group Codex, about 19 percent of Americans do 79 percent of all our (non-required) book reading. This post at The Atlantic, then, summarizes why Amazon acquired Goodreads:
And the way those avid readers find their books is changing. According to Codex’s quarterly survey (in 2012, the company interviewed some 30,000 readers total), far fewer people are finding their reading material at brick and mortar bookstores than two years ago. Instead, they’re relying more on online media (including social networks and author websites) and personal recommendations from people they know (which tend to happen in person, but can also include some social network chatting). What they’re not relying on much more heavily are recommendation engines from online booksellers, like Amazon.
I actually reasoned the numbers would be further skewed, something like 5% of Americans do 95% of our non-required reading. I would like to see more than one source for this statistic.
(Hat tip: Tim O’Reilly)