There's been a lot of talk about that recently, stirred up mainly, I think, by two things; the acquisition of Ottakars by Waterstones, and Google's plans to digitize every book ever released.
I mention the Wottakars thing, because I suspect that move is probably a sign that bricks and mortar book selling is entering its final phase, as Amazon continues to sweep up most of the trade, and the likes of Tesco and Asda take the rest.
Amongst the pros in the business, there's talk that atleast two of the five link chain (Author-Agent-Publisher-Retailer-Customer) will either vanish or merge in the next few years. And it's obvious who those two contenders are, isn't it?
I can foresee the likes of Amazon and Google buying up publishers, and in the first instance publishing printed books, sold over the net, and later on, digitally downloaded.
The latter stage requiring a must-have digital reader to be designed. And I'm sure it'll be Apple who get in first with an I-read....something easy on the eye and delightful to hold.
IMHO, the big question is: how quickly will this happen? I don't know, however, if a book equivalent of the Ipod arrived on the market tomorrow, it would certainly act as a catalyst.