Chris Matthews had a rare hit when he referred to Sarah Palin's effect on the presidential race as being like "new car smell." Lots of hubbub at the outset followed by rapidly diminishing returns. Upon her nomination I commented that she would ultimately serve to fire up the base (as if they weren't already voting for McCain) and exactly no one else; Americans are unmatched for their ability to purge their short-term memories as soon as the next shiny object flutters by. The fact is that 99% of what happens during the campaign is like new car smell.
The Palin analogy might be more accurate than Matthews intended, though, given that "new car smell" is actually quite toxic.