Could this time of year bring an increase in copper percentages? In searching boxes later in the year I seem to find fewer 2007's mixed in. I wonder if the mint dates the coins by a fiscal year rather than by a calander year and they are now making and stockpiling the 2008's to be released in January. Also people may be cashing in their change jars to help pay for holiday gifts. Just a theory, it may be only a local anomaly.
Based on the mint production figures you would think that the time of year wouldn't matter much, but for me it has. I have been seeing a lot fewer 2007 boxes as the year wears on...knock on wood. Also I'm going to try and stock up on as many boxes as I can before the 2008s hit the midwest.