When you invoke QuickLook on a folder in OS X, you are shown the folder icon along with some information about the folder. While this is convenient, QuickLook has a hidden "X-ray" feature that lets you preview items in the folder, similar to the option in Windows where pictures are displayed in the enclosing folder's icon.
To see this feature, just enter the following command in the Terminal. Then, relaunch the Finder by going to the Apple menu, choosing "Force Quit...," selecting the Finder and clicking "Relaunch."
defaults write com.apple.finder QLEnableXRayFolders 1
After you have relaunched the Finder, select a folder and press the space bar to bring up the QuickLook window. The folder should now be semiopaque and display two stacks of document previews. The stacks will flip through the various items, so you can see a running preview of the items in the selected folder.
While I do not use QuickLook on folders often, I find this feature more appealing than the default view. If you do enable the this feature, you can always reverse it by running the command again in the Terminal and substitute a 0 for the 1.