I sense some more chemistry reading coming on (it's what I really like about discussions such as this)
The term "heavy metal" is, from a scientific point of view, nonsensical; It has no strict definition. However, copper is defined as a heavy metal (or toxic metal) for the purposes of regulating industry and acceptable levels in the environment. As for toxicity levels for metals, it often depends on their state in the environment. For example, fully oxidised iron (Fe3+) isn't really an issue because it is insoluble, but sufficiently high levels of Fe2+ can lead to iron toxicity - "sufficiently high" being the operative phrase here. How much depends on many factors, including the subject in question (human, dog, etc. [lead is far more toxic to developing children than it is to adults]) and the aforementioned state (affects reactions and ability to absorb metals).
The copper in your pipes is generally covered by relatively inert copper oxide, so it doesn't really pose a threat, but if I were to feed you copper sulphate, you would become rather sick (CuSO4 makes a great fungicide). Incidentally, Cu is also an essential mineral for humans.
As for iron, I know that in wine making, contact between the must and iron is a big no-no as it leads to the formation of various iron-based compounds that add fault flavours to the finished wine. In the case of beer, I have no idea (hence some of the extra reading I need to do!).
