Lost functionality...
1) When e-mailing a "Mail Contact". Having Outlook configured to send mail in HTML. The recipient receives the message in plain text. If I delete the Mail Contact and send directly to the e-mail address, I do see bold, colors, italics,etc. (The Mail Contact is not forced to send in plain text)
2) Public folders through OWA
3) Any public folder maintenance through the GUI.
4) A very small percentage of mailboxes get a "Cannot start Microsoft Office Outlook. Unable to open the Outlook window. The set of folders could not be opened." message when opening Outlook. This problem follows the mailbox when configured on different hardware/outlook versions. If the mailbox is moved back to E2k3, everything works again. (OWA does work properly on either server)