Yeah it can. There are two ways, in the sound section of the video properties ("boost") or by holding shift and pressing the up-arrow key. Normally the QuickTime volume control widget stops you at 0db (any more than that and you would be clipping the signal) but if you hold shift and keep pressing up (up and down control the volume widget) it will go beyond 0db, even though it doesn't visually indicate it.
Geez, os x is completely riddled with tricks you 'have to know', usually achieved by some obscure key combination. Which UI book did they get this out of ? ...
The don't-clutter-my-screen-with-nine-hundred-thousand-buttons-and-menus book?
Joking aside, most OS X keyboard shortcuts actually follow a very rational scheme (which is mentioned in the Apple HIG, IIRC). If Cmd+X performs an action X, both Cmd+Shift+X and Cmd+Opt+X will perform similar versions of X, so you don't have trouble remembering "special" shortcuts.
Example: Cmd+Q quits an application, Cmd+Shift+Q logs you out and Cmd+Opt+Shift+Q logs you out without confirmation.
Another example: Cmd+Opt+Esc brings up the Force Quit dialog. Cmd+Shift+Opt+Esc force quits the current application without confirmation.
I don't think this is an OS X specific thing. I suspect Windows, KDE and GNOME all follow a similar HIG.
(No, none of those shortcuts are good for your RSI.)
