When viewing a file with QuickLook it will appear in the foreground of the screen. When you select a different window, QuickLook will go to the background. It’s possible to keep the QuickLook windows in front.
If you use Quick Look to view files that features text, you’ll notice that you can’t click and drag to highlight text. This default write command will let you click and drag to highlight text, and use the cmd⌘ + C key combination to copy text.
This command can be performd in Mac OS X Snow Leopard (10.6) and Lion (10.7) to get folders in Quick Look preview to show up with transparent covers. This option gives you an “x-ray” style view of the icons inside a folder.