I can't even begin to count the number of articles I've seen over the past few weeks about the swiftly growing popularity of tablet computers. A week or two after the holiday season has ended, I suspect we'll start seeing solid proof—one way or the other—in the form of sales numbers, and we'll finally have a firm understanding of just how many tablet PCs are out there in the world today. That'll be an interesting and even important economic factoid for the digital reading community, of course. Because as we've been reminded of over and over again, this particular consumer trend—the suddenly massive...