From time to time, one particular statistic on the inexorable rise of digital seems to stand out from the rest.  The IAB’s announcement that in H1 2009, Internet advertising outstripped that on TV is one such case.  Today came another. According to Amazon, its customers now purchase more Kindle books than hardcover books.

Amazon Chief Executive Jeff Bezos revealed the stats this week: over the past three months, it has sold 143 Kindle books for every 100 hardcover books sold. And the trend is accelerating: the ratio was 180:100 in the last month.  "Astonishing when you consider that we've been selling hardcover books for 15 years, and Kindle books for 33 months." said Bezos.

The BBC today claimed that Amazon was selling more Kindle books than hard copies (!), but that's a milestone for another day.