I did some digging around on the net and have come up with a decent idea of what will be supported. First some info on Exchange and Outlook:
Outlook uses MAPI to talk to Exchange. This allows all the data to be kept on the Exchange Server and allows for the true Client/Server environment, as in when a new email comes into a mailbox Exchange sends out a message to Outlook, if is currently running, and tells it there is a new message. Outlook does not poll Exchange every 5 minutes to see if anything has changed. That is if Outlook is running in Exchange Server Mode. All data is stored on the server and Outlook is simply a client accessing a database, you can almost think of Outlook as a client accessing an SQL database, in fact the next version of Exchange uses an SQL database as its message store.
According to Microsofts Web Page Entourage uses IMAP to talk to Exchange. This is the same as Outlook Express and Apples Mail. This is why Entourage does not have full Outlook support, but is basically the same as Mail.
From the different webs sites I have read here is what I think will be changing.
Entourage will continue to use IMAP, that will not change, way to big of a deal to be just a simple update. You will be able to store you Calendar on the server, thus letting others check for Busy and Free times. Entourage will incorporate some basic LDAP functions allowing it to check Active Directory for address info. Disruptions lists, and server stored Address Books will now be accessible from Entourage. These two items are the biggest things that will be in the update. You will also be able to sync your Calendar and the Address Books to you computer for offline use.
I do not think you will suddenly have a full Server/Client environment, or access to public folders. So this is not a huge update, but it is enough I think to let any OS X user live happily in an Exchange 2000 office environment.
