This is so true, on the Republican side anyway. All this hoopla about Iowa, and if someone wins Iowa or NH - but not SC, they are never going to be President. SC folks tend to not give a damn what folks in Iowa and NH say, and even though SC is a small state, there will be more voters in SC than in Iowa and NH combined by a big factor. A state doesn't = a state necessarily. SC is the first test of being able to move large turn out. Then Florida comes, and it's of course much bigger and a test of money to buy expensive media markets.
Iowa does help a bit. Michele Bachmann, like Democrat Chris Dodd in 2008, almost lived in Iowa for months while campaigning. (I think Dodd actually enrolled his children in school there!). After months of face-to-face meetings, hardly anyone in Iowa thought them presidential material.