Some one correct me if I am wrong, but I think the voter percentage that actually voted was something on the order of 40% in 2004. If there were no political difference between the voted and not voted group, turnout would be a wash on election outcome, but still, its a sad commentary on the sad State of the American Voter, being given the gift and right to vote, and then ducking their responsibility.
Given the fact voter turnout is historically low, all political parties hope to get out large percentages of their base while hoping their opponents are an apathetic and dispirited bunch.
The other consideration is that those who do not usually vote will mostly trend young and democratic, which is why the GOP is not thrilled with any unbiased voter registration drives or a large turnout. I am guessing at least a 60% turnout.