As part of Google's attempt to digitize all the books in the world, they attempted to count how many there are. As at 8 August 2010, Google thinks there are nearly 130 million, or 129,864,880 to be more precise.
See Inside Google Books: Books of the world, stand up and be counted! All 129,864,880 of you.
Google should call this project Google Alexandria (after the Library of Alexandria).
Of the nearly 130 million books, I have probably read a few thousand. There is simply not enough time in a lifetime to read all the books in the world.