How do I keep QTKitServer (QuickLook Helper) CPU usage from exploding out of control? OR How do I disable QuickLook entirely? I've been watching lots of .MKVs lately, opened from the Finder. In Column View, when you single-click any file, QuickLook will load a viewable thumbnail into the next column over. This causes noticeable and repeated momentary hangs in Finder responsiveness. 

I have a feeling this is related to a non-Apple-kosher file-type like Matroska Video giving QuickLook some problems. 

Has anyone had experience with this problem, OR have a way to disable QuickLook entirely? I ask because I would rather have my OS always be responsive than have CPU time eaten so that a useless thumbnail can be loaded that I never use.
Open Terminal, type:

sudo nano /System/Library/Sandbox/Profiles/com.apple.qtkitserver.sb

This will open the nano editor with the rules file. Scroll right to the bottom of this file and enter:

(deny file-read* (regex #"^.*\.mkv$"))

After this do Ctrl-O and then Ctrl-X to save and exit the application.

Reference: http://forums.macrumors.com/showthread.php?t=1463364