Apple's Mountain Lion introduced Notification Center to the Mac. This handy feature lets notification-aware apps display pop-up style alerts when something changes, like an incoming email message, Twitter mention, Calendar appointment and more.
Apple notes that you can access Mountain Lion's Notification Center by swiping your trackpad or Magic Trackpad from left to right. Alternatively, you can click the Notification Center icon in your Mac's menu bar (here's a more thorough look at Notification Center options). Those are great, but I use a third option.
Specifically, I've assigned Notification Center to a hot corner by following these steps:
- Launch System Preferences and click Desktop & Screen Saver.
- Click the Screen Saver tab, then click Hot Corners.
- Click the drop-down menu at your corner of choice, choose Notification Center and then click OK.
Now the Notification Center will appear every time you move your cursor into that corner. I suspect you're wondering why, so I'll tell you. First, I run my MacBook Air connected to an external display with the lid closed. Also, I don't have a Magic Trackpad and finally, I've been using Hot Corners for years to trigger Exposé and Spaces, so it's an action I'm used to performing.