The New Yorker (July 24, 2006) had an article by Alec Wilkinson entitled “Tenth Planet” which sort of addresses this question. (For all I know, James, this article is what inspired your post.) Caltech professor Mike Brown, who’s discovered several of the solar bodies that threaten Pluto’s status, had this to say:
“When I used to argue for eight, I felt as if there was a public sentiment that you couldn’t get rid of Pluto. If you did, you were a mean person, is what it felt like. I wondered why there appeared to be an emotional attachment to an inanimate object that most people who are arguing about had never seen. The epiphany was understanding that people love planets the way they love dinosaurs. Planets are like continents. ‘Continent’ is a good geological word, but, like ‘planet,’ it has no scientific meaning whatsoever. There is no scientific reason why Asia is a continent and Europe is a continent, and India is not. If you said you were going to take away Australia as a continent, people would not like it.
“The concept of a planet is also part of the mental geography of the world around us. Pluto doesn’t fit as a piece of science, but it does culturally. Initially, I thought, We can’t have it this way, we can’t have culture determine such questions. Then I thought, There are places where science reigns, and others where culture does. Science doesn’t have to win this one. So I thought, I’m willing to give up the hard-nosed science view of what a planet is in lieu of a cultural view, and that view includes Pluto, so it includes anything bigger than Pluto.”
That being said, for all the fulminations, I’m sure Pluto’s status matters less to most people than, say, the Red Sox’s chances of reaching the playoffs.