Could I substitute peanut butter in place of butter or crisco for cookies? In the ever-present attempt to be healthier, I've started using peanut butter in place of crisco to keep the sugars together for my cookie dough snack (sans egg.)

How would the same substitute hold up if I made a normal batch for baking?  I'm particularly curious about the melting point and the final consistency.
sometimes i'll replace 1/2 the butter in my cookies with peanutbutter and will cut the sugar a little. they still turn out pretty well. replacing all the butter would be bad, but some of it won't make much of a difference.