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UPDATE 2: Note that daylight savings time rule changes for the United States and Canada are already available in Mac OS X 10.4.5 or later. Other regions (including Australia, Brazil, the province of Alberta, Canada and several others) are affected by this February, 2007 Daylight Saving Time Update. Despite this fact, however, Apple says "You should install these updates even if your computer is used in a time zone that is not affected." -- presumably for proper interaction with systems in those regions.
Well, perhaps this didn't say what I thought it said; or maybe I read it somewhere else?