What is the percentage of independent voters in America?

According to this article written January 2nd, 2008: Independents are voters who, when asked by friends or pollsters, identified themselves as "independent" of the Democrats and Republicans. In some states, these voters can register as "independent" or "unaffiliated," but in other states, they register as Democrats or Republicans. Nationally, they make up about a third of all voters, but in some critical states like New Hampshire, they comprise over 40% of the electorate, both in general and most primary elections.

http://commentisfree.guardian.co.uk/john_judis_and_ruy_teixeira/2008/01/independents_day_1.html