Rules of thumb for fat and sugar replacements in recipes

This is my starting point for replacing butter/shortening and sugar for baking:

1 cup butter/shortening = 1/2 cup oil, applesauce, pumpkin puree, or mashed bananas. If you use sweetened applesauce, you might want to reduce the sugar in the overall recipe.
1 cup sugar = 1/2 cup honey. I haven't tried maple syrup yet, but when I do, I'll use this same formula.

Some recipes may need more or less, or may not work at all, but I can't recall any problems with this so far. I personally prefer to use oil rather than the fruit/veg purees, I included it if you want to omit the fat in your food, or increase the nutrient content (such as in the pumpkin). You can always combine these substitutes. Either way, I try to avoid experimenting when I am making something for a particular occasion.