Reason # 5,452 why I use real butter:
I had some leftover margarine after helping with a church supper (where cost was the biggest factor), and I needed to make a double batch of cookies for the auction tomorrow night. People bake with it all the time, so I thought, "What could go wrong?" I'll give you one guess as to which one was made with real butter.
And I don't have the time or supplies for a redo. :(