According to a November 2009 survey, 32% of AAUP members make content available in formats compatible with the Kindle, and 30% via electronic publication (ePub for short).
The downside to all of this is that the prequel book is currently exclusive to Amazon.com preorders and the eBook is specifically announced for the Amazon Kindle and it does not specify whether or not it will be offered in .epub or .mobi format.