I upgraded to 10.8 and cannot shake this issue at all.
I process image files daily as part of my work. For some reason only since my upgrade to 10.8, at some point Finder cannot preview any image nor can Quick Look. In order to get it back, I need to delete the DS-store file in that particular folder and relaunch Finder. This works, but eventually it will malfunction again.
I can't figure out a pattern of when it malfunctions - it happens regardless if it is new files in a few folder, old files in an old folder that was working, new files in an old files, etc.
I've had a mac for 10 years and never once had this issue, so it's a bit maddening. Has anyone else experienced this or have suggestions for a fix?