The September Cumulative Update (CU) for DST contains three changes :
For US Eastern Standard time (UTC -5:00, Indiana East), the CU adds DST support and updates history from 2006 through 2009 to reflect the change in which DST is applicable for the whole state and not per-county. Specifically, for 2005 and earlier, this timezone does not have DST. For 2006 and beyond, this time zone now contains DST.
For the Middle East standard time, (UTC +2:00 Beirut), the September CU fixes the ambiguity in the DST end-date transition time. It was the last Sunday in October at 00:00:00:000. Now its the last Saturday in October at 23:59:59:999.
For the Namibia standard timezone, the September CU updates the display name to reflect that this is a UTC +1:00 timezone, and not a UTC +2:00 timezone. However, the underlying DST rules and start/end dates have not changed. We are investigating a request to modify those in a future CU.
For more information, see the following KB article : http://support.microsoft.com/kb/2158563