December 22, 2010 thru at least December 27, it was 99 cents, as I had it featured on my blog the 22nd at that price and finally got around to the sample and bought it on the 27th.
Tracked down at least one message posted by the author about his big sale (was 99 cents for quite some time, but I don't think the entire month he said it would be):
http://www.amazon.com/tag/kindle%20b...x3QXSL4SNTKSS4