What's the value of the spoken word? $300 million, according to Amazon.com, which just purchased the leading digital audiobook reseller, Audible.com. The amount is a premium of more than 20 percent on yesterday's closing price. The purchase of Audible, which just celebrated its 10th anniversary, shows that Amazon is serious about digital content. Amazon has sold Audible's audio downloads since May 2000, and the purchase is a natural fit as Amazon offers more content via digital delivery. But what does it mean for the consumer?