There are very few things I hate more than watching a movie when large swaths have been cut off each side. Also that stupid "formatted to fit your television" message at the beginning is like a slap in the face.
While it is true that most of the time it's pretty hard to tell that stuff is missing, that makes it even more annoying when you lose letters off the edge. I'm hoping that the film was shot and produced with enough care that it's actually significant that I'm losing large percentages. And I watch movies with lots of explosions, so I want the maximum amount of bang for my buck.
There's the argument that cutting off the edges allows everything else to be larger; if you have little black bars at the top and bottom you're wasting screen space. This is becoming less important every day--screens are bigger and their proportions are closer to cinematic screens. And even if this weren't true, fullscreen is still stupid.
I watch most of my movies on a fifteen inch laptop screen. Independence Day loses a little oomph, but it would not have more oomph if it were fullscreen.
I would just like them to stop releasing fullscreen so that people can't screw it up when they buy me presents.