I am also interested in this subject as well as how folks are using Entourage for GTD. I am a current outlook user and have the plugin which works well for me -- I know there is a DA paper on setting up entourage to do the same basic tasks.
My other challenge is integrating my Blackberry Curve into the mix. I rely on the wireless synch to my exchange server which then updates Outlook for me. It would be a big step back to lose this ability and is one of the main reasons I am hesitant about dropping my windows notebook for a mac.
Are there others out there using entourage, exchange, and a blackberry who have been able to make it work without spending 40+ hours doing so?