According to the Wall Street Journal, you'll have to wait till Christmas or thereabouts. Seems the author wants to give bookstores a chance to sell the hardcover version, which was just releaased, before the eBook version enters the fray. Read about it here
http://www.readersread.com/blog/1025091
Washington Post gave it pretty good reviews so I'll probably download it as soon as it's available as a Christmas present to myself.