It's interesting to note that statistics show
revenue from book publishing increasing in all regions. Unlike music executives, who had grown used to one record-breaking year after another through the 80s and 90s, saw a decrease as evidence of lost sales due to file-sharing, publishing execs seem to think they're entitled to more even though their revenues are increasing.
I suspect a survey of serious readers (say, anyone who reads 10 books a year or more) would find that the overwhelming majority had, at some point purchased a book based on a library experience connected to that book. That could be another book in the series, another book by the same author or a similar subject. Books represent an investment in time and money and buying blind doesn't appeal to a lot of people.