Quick Look is a handy feature of Mac OS X that allows you to preview a file simply by hitting the Space Bar while the file is selected. A large preview window opens allowing you to see what the file is (provided the file format is supported by OS X.
Quick Look can open files with a simple mouse shortcut
With OS X Lion, you can open the image by clicking the small button in the upper right corner of the Quick Look window, but it’s much easier to simply double-click the Quick Look window. Not a huge time-saver, but every click saved is a click earned, I always say.