Given John McCain's and Barack Obama's ages, and Obama's "cool" branding, there was already inevitably going to be a generation gap in the voting in this year's election, but I have to believe that you are going to see a particularly sharp divide over one line: voters who are old enough to remember Jimmy Carter.
I've noted previously some of the similarities between Carter and Obama's combination of idealism, good-government rhetoric and timid and pessimistic worldview. I'm basically at the tail end of the generation that remembers the disaster of the Carter years: I'm 36 and I remember yellow ribbons and "America held hostage" and gas lines and inflation (i.e., the cost of a 2-liter of Pepsi at the supermarket kept going up) and Afghanistan and 'malaise'. I can still picture one of those Scholastic publications we were assigned in 4th grade - little red paper-covered magazine with a big graphic on the front of Carter, Reagan and John Anderson over the White House, and short summaries inside of their general positions on the major issues. We watched Reagan's inauguration in school, and the assassination attempt as well.
Carter was bad enough that you didn't need to be out of grade school to understand why. In fact, you needed a graduate degree to not understand.
Of course, it's not just Carter that Obama's a rerun of:
That's why the whole Obama phenomenon, despite some of its new racial trappings, is so comfortably familiar to GOP activists and strategists. Republicans know how to face off against Carter, Mondale, McGovern, Dukakis, Cuomo, Dinkins, etc. We've seen this movie before. Even in 1976, the GOP put on a furious stretch run as the public got a closer look behind Carter's platitudes, and he ended up winning the election by 2 points after leading by more than 30 in July polls.
PS - This is a classic. But he forgot the top level, "Commander in Chief"