One of the most desirable features in Office 2011 is the customizability of the new ribbon and toolbars. I disabled the toolbar because its functionality was substantially duplicated within the ribbon.

This presents a problem though: Once the toolbar is disabled, every now and then the ribbon tabs become completely unresponsive. There is a thread on the Office for Mac forums recognizing this problem.

The solution suggested at the forum link is to re-enable and then disable the toolbar. I have found this solution is cumbersome, time consuming, and often does not address the issue.

I found that if you click on the very top edge of the unresponsive tab, it will select as expected. Here's a screenshot.

I have submitted a bug report to Microsoft, as I am sure others have, and hopefully this bug will be fixed soon.

[crarko adds: I haven't tested this one.]