For problems of an urgent nature, contact Microsoft CSS/PSS.
If you applied the time zone patches on Exchange server and all clients, and the Exchange CDO patch on Exchange server, you generally shouldn’t see such issues.
However, if new computers pop up on the network (or old ones are rebuilt) without the correct time zone updates, and these are used to create meetings – the appointments get created with the older timezone data.
Other considerations: mobile devices like BlackBerry and WIndows Mobile that are used to create/modify meetings. If these do not have the correct time zone information, you will have such issues.