Having been through ~2 semesters of calc, I have been trying to think of good ways to apply what I have learned, other than in newtonian mechanics.
Thus, for those who have taken calculus, what have you found incredibly useful, if not fun???
-Joe
Well, I can’t think of anything at the moment…I think I learned something… 
but here’s something interesting:
The solid created by the graph of 1/x rotated around the x-axis has finite volume but infinite surface area. As my math teacher said, you can fill it with paint, but you can never paint its surface. This “paradox” is known as Gabriel’s Horn.
I like calc. If nothing else, its a great step into higher level problem solving.
As for individual concepts… I feel I benefited from all of the vector stuff, as well as integration and differentiation concepts for signal processing.