Because of the thickness of the glass, a matte film will make the display fuzzy. A matte display is not fuzzy at all, though (anyone who says so hasn't used one). A film also won't reduce reflections since the glass behind it is reflecting just as much light, so the diffuse reflected light from a glossy display with a matte film is more than that from a real matte display. In short, a matte film over a glossy display is the worst of both worlds.
I do keep a matte film on my iPod for the sole reason that it makes the touchscreen feel more responsive since the friction is more consistent. I don't even need it for the scratch resistance since in a year with no screen protector there isn't a scratch on the display (the back is another story).