Variable daylight saving time sucks. Here in Israel it causes problems every year. Meetings are missed, IT staff go over all their systems, and clock owners go berserk. Since Outlook appointments are relative, changing the clock affects their schedule, especially in a multi-national organization.
So, how to fix this? The Microsof Exchange posts about this issue, focusing on Brazil (I wish they would focus on Israel, but you can't really have it all).
Read it here: