Initial reports from New Hampshire is that voting is very heavy, particularly among Democrats. As in Iowa, the weather is cooperating.
One of the key variables in NH is registered independents, who can participate in either contest. In Iowa, indies chose by a three-to-one margin to caucus with Democrats, though some observers argued that the extraordinary attention the Dem candidates were paying to the state, and the virtual absence of two major GOP candidates (McCain and Giuliani) skewed those numbers. NH will be a better test of indie partisan leanings, since if anything the Republican race is perceived as the closest.
If Barack Obama wins the Democratic primary, as most late polls predicted, a lot of attention will be paid to any evidence that his campaign had a tangible impact on turnout, particularly among indies and/or first-time voters.