We have a UM Unity 4.0.4 Failover Environment. MWI worked fine when integrated with Ex2000. We have migrated all users to a new Ex2003 environment and re-integrated Unity with it. MWI's are very sporadic....quite often delayed by 5 or more minutes turning on or off, sometime never sync correctly at all. Funny thing is that I can refresh the status on any subscriber and the light will respond correctly.
btw...our Outlook 2003 clients are using cached mode.