PaidContent reports that while lots of people are buying books online, most people aren't learning about those books online:
Sixty-one percent of book purchases by frequent book buyers take place online, but only seven percent of those buyers said they discovered that book online, while physical book stores account for 39 percent of units sold and 20 percent of discovery share: the stats come by way of new research from Peter Hildick-Smith, the founder and CEO of the Codex Group, which tracks frequent readers’ book-buying behavior. At the Digital Book World conference in New York on Thursday, he said that discovery and availability are being “decoupled” online. In other words, readers are likely to go online to buy a book after having learned about it elsewhere.
It's virtually impossible for an online bookseller's recommendation engine to surprise you with a book suggestion. You need real, live human beings to introduce that special kind of randomness into the equation.