Before the "Erhmegherd Copper is toxic!!" circlejerk goes too far, please read this comment from the copper spoon thread:
Alright, I'm seeing a lot of sort-of science and misinformation here. Here's how copper interacts with other things to poison you.
Copper doesn't dissolve easily. In its native form, copper is unionized and fairly stable, just like other precious metals (silver, gold). However, copper ions, if integrated into the body via ingestion or inhalation, are very bad for you. Not quite lead bad, but still very bad.
The danger comes not from copper metal, but copper oxides. When copper oxidizes, it bonds ionically, meaning copper ions bond with oxygen ions to give you copper oxides. This is the stuff that makes pennies ugly. In small quantities, it gives copper that dark dull brownish color, but in high quantities, you get that green coppery color the pennies under your couch have. In the arts world, it's called patina. If the same process happened on your car, it would be called rust. Technically the green growths are called verdigris.
Copper oxides are relatively stable, but remember the copper is in the form of a positive ion, and the oxygen in the form of a negativei ion. Acids are measured based on how many positive H ions they have in them. The more H+, the stronger the acids. When a strong acid comes in contact with the copper oxide, the H+ ions can strip the oxide off of the copper, creating Cu+ and H20. This is why if you put a copper penny in a glass of coke, it will get shiny. Unless it's cocaine, then it will just get covered in cocaine. Anyway, the citric acid in the coke is a relatively strong acid when it comes to food (although it is a weak acid overall). As a result, it can pull the oxygen atoms off the copper oxides and "deoxydize" the copper). While this makes the copper pretty, it means theres also a bunch of Cu+ floating around the glass now, which is the bad kind of copper that can hurt you.
Generally, this means that there are two rules to follow when using copper for utensiles. Follow both, and you'll be just fine.
Don't cook heavily acidic foods in copper
Keep it shiny.
On the first count: Don't cook heavily acidic foods. This means foods involving citrus or other fruits. Especially involve cooking things with tomato or lemon, since they are very acidic, to the point that they pull enough Cu+ into the food to alter its taste (tomato sauce + copper pot = the taste of a dirty penny). Even meat is mildly acidic, but might be ok, I'm not sure because I prefer to do my meat in a cast iron pan anyway so I never looked it up. Leafy greens are not acidic, neither are root vegetables.
Next, Gorram it keep it shiny. You hear? Regular elemental copper does not dissolve well in the presence of acids (It does to some degree, but not nearly as much as copper oxide). If you can see your reflection in the copper, its polished. Keep it polished and free of oxides and you will greatly reduce the amount of Cu+ ions you are ingesting by using your favorite copper cookwear.
It is possible to use copper cookwear safely. It's very popular with cooking aficionados for the sake of sauteing vegetables, and its very popular in the brewing and distilling hobbies. Just know how to use it and how to use it properly and safely. Like they say, arm yourself with knowledge
Source: science student, cooking fan, amateur coppersmith, will probably die due to inhaled copper particles