Following are names and descriptions of the sub-folders and their contents in the Preference folder.
The MRU (Most Recent Used) folder contains listings of the last saved files in the Preferences folder. These are used by the Dejavu XTension. If you don't have the Dejavu XTension loaded, you have any files in the MRU folder.
This is the cache folder location for full resolution preview of an image in a QuarkXPress layout. Caching is done by the Quark Image Engine to generate an image cache on disk. It then uses the Picture Import engine to re-import the higher resolution image preview into the picture box. It saves the cache information for every image in the Preview Cache folder.
PSD Import Cache
The PSD Import Cache is controlled by the PSD import filter. It is used to avoid memory problems while importing memory intensive .PSD (Photoshop) images. A Temp file (tmp) will be generated in this folder for every PSD image imported into a QuarkXPress layout. Changes made in the image in QuarkXPress are cached in this location.
PS Profile Cache
PS Profile Cache contains information about Applied and Destination profiles. It retains Quark Generic profiles information in the Cache. If you applied any Quark Generic profile, cached information will be saved in the folder. The reason why PS Profile Cache folder is required is that, every time you apply Generic profiles, QuarkXPress generates a cache of this information.
QLog folder is related to log management. When you launch QuarkXPress, it specifies trace information to the log. This can be very useful when reading a QuarkXPress Crash Log.