See Icon Previews in Folder Quick Look Windows
I demonstrated today's OS X hint (which works in both 10.5 and 10.6) in my latest Snow Leopard tips video, but for those who prefer their hints in the old-fashioned text format, I'm repeating it here today.
Quick Look, the "sneak peek" feature that shows you the contents of a file when you select it in the Finder and press the Space Bar, has a hidden capability for working with folders. Normally, using Quick Look on a folder is sort of boring--you see a big blue folder icon, the size and number of items in the folder, and a last modified time.
But with a simple Terminal trick, instead of the boring blue folder icon, you can see the boring blue folder icon...with cycling animated icons representing each of the files within the folder. To enable this feature, open Terminal, paste in the following command, and then press Return:
defaults write com.apple.finder QLEnableXRayFolders 1
To make this change take effect, you need to relaunch the Finder. There are many ways to do this, but one of the easiest (and cleanest) is to hold down the Option key, then click and hold on the Finder's Dock icon. When the contextual menu appears, select Relaunch.
Now select a folder in the Finder and press the Space Bar, and revel in the icon previews.
If you tire of this eye candy in the future, open Terminal again, paste in this command, and press Return:
defaults delete com.apple.finder QLEnableXRayFolders
Relaunch the Finder again, and Quick Look will be back to its stock treatment of folders in Quick Look mode. Thanks to Mac OS X Hints reader freaktheclown for discovering this one.