If I patch my Exchange server both with the OS update and the patch for Exchange 2003 SP2 (KB926666) BEFORE patching all workstations, will users at those unpatched workstations see their appointments shifted by an hour? Everything I've read states that the determination of how an appointment shows up is based on the client time zone from which the appointment was created. Will patching my Exchange servers also shift the time of these appointments?

No, it will not .. it depends on time zone of cients if You use Olk2k3

On the flip side. What if the clients had their OS patch backed in January when the patch was released. However, the Exchange server hasn't had the OS Patch or the CDO patch applied. When those Excchange patches are applied this weekend, will the appointments shift by an hour? It would seem that since the clients were aware of the new DST rules when the appts were created, there wouldn't be a shift after Exchange is patched?(This is of course assuming that the appts were created in the extended DST timeframe while the client was aware of the new DST rules.) Thanks for any thoughts on this.

I didn't test deeply, but it's about that timeframe you meaned. You can have mixed nations on exchange organization (each worksation can use diverent time zone) and that is why the timeframe is filled by client side...