It's a tough job, but somebody's got to do it: find overlooked OS X tricks. Sometimes I hunt for them; sometimes I just run across them. Here's a collection that I bet includes items you've missed, too.
1. Force Quit the current app
Pressing Shift before or after opening the Apple menu changes the Force Quit command to Force Quit [Current Application]. By reflex, I've always pressed Command-Option-Escape, selected the frozen app in the dialog box if necessary, clicked the Force Quit button, clicked the confirming dialog box, and then closed the window. But now I'll use this menu trick to save myself those extra steps.
The menu shows a keyboard shortcut for force quitting the current application. But don't get too excited: I've tried the shortcut on five different computers in Lion and Mountain Lion to no avail. Only choosing from the menu works.
2. Take a break from notifications
Want some temporary relief from those helpful, yet intrusive, notifications from Apple's Mail, Calendar, Reminders, and other apps? You don't have to turn each one off through System Preferences, because there's a hidden On/Off button.
Clicking the Notifications icon in the far right of the menu bar or using a two-finger trackpad swipe (starting at the far right edge of the trackpad) opens the Notifications pane. There's no clue that that you can pull it down past its topmost category, but you can, using a two-finger swipe. With a mouse, use the pane's scrollbar or the silliest Apple interface action ever: press (that is, hold down the mouse button) on the header for the topmost category until the pane scrolls. Then, you can turn off Show Alerts And Banners.
As a reminder of its Off state, the Notifications icon turns gray in the menu bar. Notifications helpfully turns itself back on the next day so you won't forget to reactivate it.
And now that you know what happens in the background, here's a shortcut: You can quickly turn Notifications on and off temporarily with a simple Option-click on the Notifications icon.
3. Empty the Trash from the Dock
You don't have to go all the way up to the Finder > Empty Trash menu if your cursor is down near the Dock. Control-click the Trash to get a short menu with an Empty Trash command. If sensitive data is an issue and you want to erase your files more securely (the standard Empty Trash command leaves information that can be recovered with special utility software), press Command before or after opening the Trash menu for the Secure Empty Trash command.
4. Relaunch the Finder
When you have trouble in the Finder--it freezes, or windows go wonky when you change views--relaunching it is an almost sure-fire cure. Access the Relaunch command by pressing Option and then clicking the Finder icon in the Dock for its menu. (Unlike other Option-key Dock menu changes, this one requires that you press Option before you open the menu.)
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