A WebmasterWorld thread is reporting seeing an spike in the number of instances Google is showing Google Book Search results within the web results. A few other members have agreed in seeing a larger number of book results in the Google web results.
Robert Charlton speculates Google may be testing if searchers like these results. And based on click data, they may decide to keep the results more prominent or not.
I think it is a seasonal thing. As one member points out, "these have been there for weeks and are increasing their density by the week." What is about this time of the year? Back to school maybe? In fact, almost exactly last year, we reported the same exact issue. Last year on September 24th I wrote, Google Book Search Results in Google.com Organic Results? It was discussing how members noticed an increase in book results coming up.
Google started experimenting with Google Book Search results in web search back in December 2004.
So do you think this is a seasonal thing for back to school season or just a test?
Forum discussion at WebmasterWorld.