Skeptic--If you ever decide to pursue improvisational baking, look up Ratio:Â The Simple Codes Behind the Craft of Everyday Cooking, by Michael Ruhlman. Most of the first 85 pages are about the baking ratios of which Mike speaks.
When it comes to yeast breads, I am comfortable shifting around and substituting. I have been able to do more than I had hoped with quick bread and cake recipes where I need to substitute oil for butter. However, I accept that there are some recipes--those with lots of butter--for which I will not be able to create a less saturated fat version.