Lonespark's annoying friends on facebook made me think of this. Before you think I'm being mean, Lonespark told me to say that.
So, arithmetic. Mathematicians use calculators. We don't need to add subtract, multiply or divide particularly well. When long division becomes useful is when the things being divided aren't numbers anymore so some of us don't even bother to learn it until then.
Arithmetic is this tiny tiny part of math that we're generally not terribly concerned with, but it is vitally important. It's like learning to be able to distinguish between letters. Advanced literary criticism isn't about telling the difference between b, d, and q, but it's kind of a necessary foundation if you want to do advanced literary criticism. Obviously different letters for different alphabets. But whether it's Arabic or braille, being able to tell which letter is which is an important foundation.
Arithmetic is like that. You get through it, you try to learn it to the point you don't have to think about it to do the basic operations, and then (hopefully) you never think of it again.