In the U.S., we go off DST this weekend. Mac OS X since 10.4.5 has been ready for the new changes in the U.S. Daylight Saving Time rules for 2007, that is DST started on March 11th and ends on November 4th. In version 10.4.8, Apple added additional recent changes for other countries. As a result, in the U.S., anyone with Mac OS X 10.4.5 or later will be ready for the weekend change.
For more information on Appleis Daylight Saving Time OS changes, see Apple support article # 305056. That article also references a fix for those still using 10.3.9.
For more information about Daylight Saving Time in general, see the Webexibits page or the U.S. Naval Observatory site.