Last night on my RDS server (Server 2008 R2) I upgraded Office 2007 to Office 2010 and Outlook has no ribbon. It's even missing the tab titles in the minimized ribbon view. That is, on my machine, when the ribbon is minimized I can still see the tab titles. On the server there are no tabs.
I have not found any relevant searches on Google or this site and I've tried restarting the server as well as deleting a user profile. Unless there is a way to bring it back my next option is to uninstall/reinstall.
My Outlook with ribbon minimized:
Outlook on server with ribbon minimized.