“E-books now account for about 20% of the market — more than double a year ago. An even bigger surge is expected this week and next month, with people unwrapping their new e-readers and tablets. In the next few years, e-books are likely to match print sales and eventually overtake them. For readers, books have never been more accessible or plentiful. But no one is sure what it means for traditional publishers, authors and bookstores.”