Starting Wednesday, April 1, 2009 between 00:00:01 PT (12:00 AM plus one second on Wednesday, April 1, 2009) and ending on Tuesday, April 14, 2009 at 23:59:59 PT (11:59 PM plus 59 seconds).

This is good for up to 10 items, potentially saving you up to $40!  There is a list of exceptions which can be read here.