In an blog note (http://macte.ch/ZSLei), the Office for Mac team at Microsoft says that Office for Mac 2011 is compatible with Mac OS X 10.8 Mountain Lion. However, it doesn’t support full screen mode, iCloud or Macs with Retina display. Regarding the latter, only Outlook for Mac 2011 will be able to take advantage of the higher resolution.
That said, if you do use Office on Mountain Lion, Microsoft says you should note the following:
° Make sure you have Office for Mac’s AutoUpdate enabled – some updates will be needed to make the most of the upgrade to Mountain Lion. Initiate AutoUpdate in any Office for Mac application by going to your toolbar, then selecting “Help” and then “Check for Updates.”
° Mountain Lion ships with a new feature called Gatekeeper. Gatekeeper helps protect users by allowing you to choose to only download and install software from known developers, like Microsoft. Please note that due to the Gatekeeper architecture, updates will not run when you download and initiate them on your desktop; instead please use Microsoft AutoUpdate to keep your copies of Office for Mac current.