It should be pointed out that Quick Look plug-ins reside in memory at all times. If poorly coded, they can cause the QuickLookHelper process to consume inordinate amounts of RAM, hang or crash. Make sure you review your plug-in of choice. For instance, a text-preview plug-in that matches all unknown file-types can seem incredibly useful, but it might end up slowing down directory listing in Finder.
Good tip. NOT installing all, then.