Another take on GM foods:
As I see it, the real root difficulty with GM foods, as with many other technologies such as computers, medicine, and even the automobile is not just that of trust and accountability on the surface, but also of relative ignorance relating to science in general on the part of the consuming public.
We tend as a society, to specialize. Part of this has been a result of the sudden bloom of information brought by scientific and technological advancement. The expanding foundation of general knowledge required for the average person to have a fairly solid idea of how each technological process he or she uses on a daily basis really works has left many of us in specialized niches, but with vast holes in our understanding of the modern world. So we must trust. I program computers, and have a general interest in most everything, but that doesn't mean I can (for instance) repair an engine or prune a tree with any degree of competence or efficiency, so like many others, I count on the trusted advice and services of other individuals with different specializations.
In an ideal world, as Heitah states above, if Genetically Modified foods were to be labeled, the only sensible way to go about it would be to explain directly what aspects of the source organism had been modified, and what non-standard chemicals are present, and in what concentration. At that point the intelligent and well informed consumers comprising the Market would evaluate the labels and make their decisions based on that information and any partiuclar needs or preferences they might have.
In our less than ideal world, most consumers either don't know enough about nutrition or biology, or couldn't be bothered to put in the effort to find out, so the labels would be meaningless to the majority of people who might encounter them. While they may be meaningless, they may still trigger an aversion response among those who know that they do not understand the technology and are therefore uncomfortable with it, or maybe have been persuaded by somebody at some point or another that GM foods are inherantly harmful. So if you have labeling without accompanying education you have catered to the small minority who understand the technology, and you have also stirred the most base instinct of fear among those who do not understand the technology. Clearly that will get you nowhere in terms of progress, and if you are in the business of distributing GM foods, it would not help your pocketbook at all.
This puts the makers of GM foods in an interresting bind. If they do not label their product, they are accused of deception, yet if they do label these products, their market share decreases drasticly as the majority of the public will never read past the first line in the label. Ultimately this is what many opponents of GM food are reaching for, an economic disinsentive, a force to dissuade people from attempting these experiments to begin with.
I personaly have nothing against GM foods, and on the rare occasion where I find sufficient documentation to convince myself of their safety (I will note that this case is rare not because I have found any that are unsafe, just that the documentation (for reasons described above) is rare) I experience no hesitation when buying such foods. I feel that their widespread adoption will not come until a time when the public is generally well informed enough to evaluate their safety without having to trust the word of the designer or grower. This may come in stages (first, (at least in the United States) FDA or USDA regulation and some sort of safety approval process where GM foods that have been approved will bear some stamp or label asserting that they have been evaluated and found not to be a health risk), and then maybe if that utopia ever arrives where human beings will all be well versed in the sciences and have a healthy general knowledge of the functioning of the world around them, eventually labels will only need to bear the nature of the modification, and as we now take literacy for granted, the common grocery shopper would be quite able to understand.
Not addressed here are the economic and philosophical questions. Those are seperate debates. My feelings are that the Intellectual Property laws in general will need to change once information (be it in the DNA of a plant seed, or stored on a computer, or printed in a book) becomes better understood as an economic commodity. This will effect much more than seeds. As for the philosophic arguements, I'd rather stand clear and not muddy the scientific questions with claims and conjectures which by definition cannot be proven.