Apple previously made changes to Mac OS X 10.4.5 to account for the change in the 2007 date for changing to Daylight Saving Time (DST) in the U.S. and most of Canada. However, the Mac OS X update Apple posted on Thursday also makes reference to fixes for DST. The reason for the second fix is described in Apple KB article # 305056 which was updated on Thursday.
The KB article explains: "... the 2007 time zone and Daylight Saving Time rule changes for the United States and most of Canada are already available in Mac OS X 10.4.5 (released February, 2006) or later. However, some additional regions that recently adopted time zone and DST changes are available in the February, 2007 Daylight Saving Time Update, detailed below."
These other regions which had DST rule changes (as of January, 2007) include: Australia, Brazil, the province of Alberta, Canada and several other regions.
The KB article has additional information for users of Jaguar and previous versions of Mac OS X as well as Mac OS 9.2.
More information about the DST in general and the 2007 changes are at WebExhibits.