The Brewing Network.com - :
talks about copper in your brew.
Found through google search here
in which a summary is posted "In a nutshell, drinking water in copper pipes, or boiling wort pre-fermentation in a copper vessel (or with a copper pipe in the boil pot). the amount of water contacting the copper is limited to the time the water is passing through the pipes or boiling in the kettle. The pH is pretty neutral (though it drops as the boil goes on). There's not a lot of contact time, so not a whole lot of copper goes into solution. What small amount does, the yeast take it all out during fermentation. (The copper is a good nutrient for yeast). Using copper in the fermenter or afterwards is during a period of lowered pH and the copper will continue to dissolve into solution as fast or faster than the yeast can consume it. Sulfates in the water will bind with the copper producing copper sulfate, a poison. I highly recommend the podcasts."
That said, it's probably ok to have a LITTLE bit of copper in your fermenter...