It seems that Obama not only appeals to younger voters, but actually gets them to turn out. I am reminded of events between 1968 and 1972. In '68, Sen. Eugene McCarthy managed to get a whole bunch of long-haired hippies to go Clean For Gene, cutting their hair and going door to door in New Hampshire in suits. This same phenomenon carried over to Bobby Kennedy's campaign as well. It was the death of the latter that really spelled the end of youth support for any Democratic ticket that year.
Yet, the phenomenon was noted by party leaders, who saw a possible opportunity at gaining a whole new cohort - college kids disaffected by the draft and the war in Vietnam. They managed to push through a Constitutional Amendment lowering the voting age from 21 to 18, the theory being that they were seriously effected by national policies, yet disenfranchised. The results weren't quite what were intended. Not used to voting, more concerned with the drudgery of discovering the trials and tribulations of living on one's own, the sudden increase in the electorate had two effects - lowering the turn-out percentage, and discovering that there were youth who might support Republicans. 1972 was the first year 18 year olds could vote, and while certainly noisy in the McGovern campaign, nationally (like all other age cohorts that year) they supported Nixon. In the years since, this age group has the lowest turn-out rate of any, and they tend to split fairly evenly between the parties.
Obama, however, seems poised, possibly, to change that dynamic. Of course, like with all things, we shall have to wait and see, but if this trend holds, this could be the biggest political story of the 2008 election cycle - the Year of the Youth Vote.