Pearson, Inc is the parent company that owns Penguin and Pearson Education. They are the world leaders in trade and educational publishing, respectively. It also owns the Financial Times, Dorling Kindersley, and other ventures. Their 2010 numbers were just released. One point in particular is of relevance to people like you and me:
Last year  almost 30% of all our revenues were for digital products (42% if you count those blended paper/digital programs). Our digital education platforms now serve almost 60 million students, up 43% from last year.
Let that soak in a little bit. The LARGEST publisher in the world made 30% (or 42% if you prefer) of its revenue from digital products. And the fact that they differentiate between digital and digital/print blend is HUGE. These aren't fudged numbers. Pure digital content made up nearly 1/3 of the revenue of an $8.7 billion year.
That's 2,610,000,000 dollars in digital revenue. 2.6 BILLION.
The digital age is here, my friends. Welcome to the future.