"Amazon reports that sales of e-books have finally surpassed sales of hardcovers. That's a pretty momentous development." Megan McArdle at The Atlantic thinks the Kindle's day has come. "I think it not only means that e-books are entering the mass adoption phase, but also that the price-discrimination model that publishers have used for decades may be on its way out," says McArdle. "There's no significant benefit to buying most disposable mass-market books in hardcover; people do it because they don't want to wait for the paperback."