One gripe I hear a lot from OS X Mountain Lion users is that they sometimes get notifications bothering them at the most inopportune times. I know that when I'm working on TUAW TV Live, the last thing I want is something else to distract my attention when I'm already distracted by about 15 other open windows. Author and tip maven Saied Ghaffari was showing me one of his e-books the other day that included a very useful tip on how to temporarily shut off those annoying notifications in Mountain Lion.
To do this, simply press the Option key and click on the Notification Center icon at the far right end of the menu bar. The icon turns grey to indicate that those banners, sounds and alerts are not going to harsh your mellow.
When you're ready to start getting notifications again, do the Option-click on Notification Center dance again and the endless parade will continue.