I have to agree with sacre on this issue. Meat causes cancer, vegetables cause cancer, milk causes cancer..... I stopped caring a LONG time ago, because it seems that nearly EVERYTHING increases your cancer risk, even things that you need in order to survive, like food and even WATER.
They don't need to put warning labels on these carbon nanotubes, unless they are prone to breaking up and becoming airbone. EVEN THEN, they should only put a warning label on it if LARGE amounts of these carbon nanotubes are known to become airborne from something.