This is a very simple little trick which you can enable in Snow Leopard. In essence it provides a thumbnail preview of the contents of any folder. This is quite useful for quickly looking inside a folder. All it involves is a simple Terminal line.
The first step is to disable any Quicklook plugins you may have installed. For example you may have installed the Folder Viewer. This is found in /Library/Quicklook . Simply delete the .qlgenerator file or move it out of the folder. This will remove the plugin from the Quicklook program. The next step is to apply the Terminal code.
Open up Terminal, located in Applications > Utilities. Copy and Paste (or type) the following.
defaults write com.apple.finder QLEnableXRayFolders 1;
This will apply the code to enable previews and restart Finder for the changes to take effect. Its not that useful, however if you don’t have a plugin it can be an added bonus. Since it runs using Quicklook any file preview will be rendered.
Its fun to enable, however I recommend installing the Folder Viewer as mentioned in the begging of this post.