Time magazines’s Josh Quittner offers some insight into Kindle sales:

According to a source at Amazon, “on a title-by-title basis, of the 130,000 titles available on Kindle and in physical form, Kindle sales now make up over 12% of sales for those titles.”

Amazon’s quarterly results didn’t spell things out more, though the inventory of eBook titles continues to grow:

The number of titles available for the Kindle are now up to 140,000 compared to 90,000 at launch, and the company did not break out any other Kindle figures except to say sales of e-books represent a low double digit percentage of the 140,000 titles available in both e-books and print formats.