The U.S. Kindle Store now has over 700,000 books. This is up from 670,000 books three weeks ago. It seems like Amazon is adding books to the Kindle store at a steady pace; As of the end of April, the store had 500,000 titles. The U.K. store only has 400,000 titles, as of our last report. Barnes and Noble claims to have 1 million titles for purchase.