We've been working with Apple to ensure a fantastic experience for our users. There are a couple of items we'd like to call to your attention:
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.
You can get Mountain Lion on your Mac by following these instructions.