I don't mean to turn your question into a separate discussion, but I've seen Entourage absolutely wreak havoc with Exchange 2003 calendars. I've seen Entourage repeatedly overwrite and delete calendar entries, presumably because it thought its data was correct and the Exchange server's data was not. This situation was complicated significantly by multiple delegates running Microsoft Outlook, as well as BlackBerry Enterprise Server and multiple copies of Entourage (on different Macs) accessing the same mailbox. I wasn't close enough to the situation to have called Microsoft, but from what I gather, they weren't able to provide solutions.
This may sound crazy, but I'd actually recommend Parallels or VMware Fusion and Outlook 2003 or 2007 over Entourage. I believe (but don't know for sure) that was the ultimate solution in the above-mentioned case.