lucy24 - 9:16 pm on Aug 13, 2011 (gmt 0)
If it's already there but you suspect people are overlooking it, make them notice it. Er, I mean, make it noticeable, not grab them and rub their noses in it ;) Something with an arrow saying "figure your shipping rate now", that kind of thing.
As a human user, I often do have to start the checkout just to learn the shipping rate. So your reasoning sounds solid.