OS X tips
Calculator – hidden features
Screenshots – additional features
Shortcut for secondary dialog buttons
Quit from the dock
Switch to app and hide others
See full text of truncated file names
OK, the features aren't actually hidden, but most people may not be aware that there's a lot more to the Calculator than just the simple math calculations. Select "Advanced" under the view menu (Command-2) to view all the advanced math calculations. There's also a "Paper Tape" feature that keeps track of all your entries. But the most surprising feature of the Calculator is under the "Convert" menu: Here you can convert currency, area, weights, and much more.
Screenshots – additional features
In 10.2x, if you hit command-shift-4 and then hit the spacebar once, your cursor changes to a camera. Click on any window, menu, menu bar or Dock region you want, to capture only that window, menu, menu bar or Dock region.
The object you point the camera cursor at will change colour to indicate what you will capture. In the Dock, the region captured will be indicated by a pale blue rectangle.
If you want to capture a menu, you will need to toggle it open first
by clicking it before you hit command-shift-4.
Hitting the space bar again will toggle back to the normal region capture
mode.
Add the Control key to capture the image directly to the clipboard (also works with command-shift-3 and the normal region capture mode).
Hit the Esc key to cancel out of screen capture mode.
Shortcut for secondary dialog buttons
Use command-. (period) to access most secondary buttons in dialog boxes, even if it's not "cancel". For example, when you change the extension of a file in the Finder and it asks you if you want to really keep the new extension, the default button is to keep the existing extension, so use command-. to access the secondary button that applies your new extension. To access "cancel" in most dialogs, simply hit the Esc key.
To quit a running application without having to switch to it, control-click on an application's icon and select quit. If you have full keyboard access turned on, it's even better, because you can access the dock and then use your arrow keys to select icon after icon and simply hit the Q key to quit multiple applications (hit the H key to hide an application instead).
You can switch to an application and hide all other visible applications in one click: command-option-click the icon in the dock. When using full keyboard access, select the application's icon and hit command-option-enter (not return).
See full text of truncated file names
The Finder truncates long file names in list and column views. To see the full file name, hover your mouse over the file name for a few seconds, or hold down the option key to see it immediately.
Use British spelling in your searches