Originally Posted by quilter1

There is a difference between 'sour' milk and milk that has gone bad. Milk in the stores has been pasturized so when it curdles and smells bad-- it is bad and I would not use it. 'Sour' milk has been soured by adding something to it that thickens it, like vinegar or lemon juice. Buttermilk on the other hand is the 'milk' left over from the butter making process, that is why it is low in fat. Sour cream is commercially made from fresh milk products. These products always call for baking soda to be added as it will interact with the acid in the milk product and cause the cake or pancakes or whatever to rise.
If you used 'sour' milk by mistake and it wasn't curdled or didn't smell bad, then I think the cake is likely OK to eat, it would be cooked. If it was lumpy and smelled, then I would toss the cake. Why take a chance?