Really good cake...from a mix!

I made a good discovery yesterday- I was making a cake (from a mix, of course), and realized I was out of cooking oil. But I remember reading in the Joy of Cooking that you can substitute melted butter for oil (actually it was the other way around). So I used melted butter, and the results were fantastic. The cake was sooooo much tastier than usual mix cakes: moister, more flavorful and more "held together". Just thought I'd pass on my new baking secret, since I don't have many of them.