I found this tiny software kind of useful when you have very high res displays like i do. I have an Hi-Res 17" MacBook Pro and a 30" Dell Ultrasharp display and I use them both at the highest resolution. This sometimes causes problems when I watch low-res movies like standard 640x480 letterboxed MPEG4 that don't perform very well when viewed at full screen.
With Wide Screen Movie Player you can easily set the size of the player while keeping a nice black background that doesn't disturb your eyes.

For what I have seen the application basically creates a black windows that embeds a quicktime player that you can resize inside the container using keybord shortcuts or the menu bar. the window can be set at full screen hiding the dock and the menubar. stretching the embedded qt player have a slightly different behaviour than switching quicktime to full screen mode and i found it better. the problems arise when you try to zoom the actual content. that is pretty useless since the videos become unwatchable and out-of-sync even on a 2.4 dual core macbook pro.

the licence is definetly too expensive for what you get