I came across this population study (Framingham Heart Study) which looked at the different rates of heart disease with varying intakes of butter or margarine. See the chart below.
The results show a lower incidence of heart disease in the butter (saturated fat) and a higher, increasing rate of heart disease for margaine (unsaturated/trans fats). Here is the link to the study abstract: http://www.ncbi.nlm.nih.gov/pubmed/9229205
This is one of many studies that refutes the idea that saturated fat is so bad for you (of course I am reviewing only one study, and one study doesn't prove anything). It brings up the questions: why do infants need such a high saturated fat content in their milk and why have so many civilizations eaten such a high level of animal fat in there diet and not developed heart disease, but in the last half century, saturated fat has suddenly become deadly for Americans?