>Enable See-Through QuickLook Folders

I find this super useful and so I thought I would share. (source: http://www.thecustommac.com)

Enable See-Through QuickLook Folders

OCTOBER 7, 2009

Open Terminal and type in

  defaults write com.apple.finder QLEnableXRayFolders 1

Then enter

  Killall Finder

to restart the Finder. You should now be able to quicklook any folder that has files and see it in the folder preview.

UPDATE: If you ever want to disable it this feature, quit the Finder, then repeat the above Terminal command, but change the 1 to a 0.

Source: Mac OS X Hints