Here's a piece from The New Republic which argues that Dean's main weakness in a general election would be his secularism. The article is both commonsense and horribly depressing at the same time (thanks to Matt Yglesias for the covert non-subscriber link).

For example:

One day, a truly secular candidate might be able to run for president without suffering at the polls. But that day won't be soon. This is, for better or worse, an openly religious country that prefers its politicians to be openly religious, too--a trend that has only become more pronounced in recent national elections. A 2000 poll by the Pew Research Center for the People and the Press found that 70 percent of Americans want their president to be a person of faith. This religious vote isn't just concentrated in Southern states that a Democrat has no chance of carrying. It also saturates the Midwest, where Dean would have to win to have a chance at the presidency. (According to the American Religious Identification Survey, only about 15 percent of respondents in Wisconsin, Iowa, and Illinois describe themselves as nonreligious.) Indeed, in the last five presidential elections, the candidate who more aggressively conveyed his religiosity (whether honestly or not so honestly) won. Seen in this light, a popular contest between Dean's secularism and George W. Bush's heartfelt faith could be, well, no contest. And the same, in turn, could be true of the election.

I think Dean would lose mostly because he's incoherent, inconsistent, and grumpy. But the article's probably right that his lack of religion won't help either.

I've heard comparisons of Dean to McGovern, but as the TNR piece illustrates, comparisons to Dukakis are much more appropriate. He's a liberal, northeastern governor, the fantasy President brought to television in the West Wing (though that fictional Commander-in-Chief is a Catholic), but one that won't make it into the White House anytime soon.

The article talks about how Clinton parlayed religiosity to win a healthy chunk of southern votes. Say what you will about the man, he was not politically dumb.

Dean has done some very smart things politically so far, but this is the area that's going to come back and haunt him if he goes up against Bush.

I wish we didn't live in a country where this is even an issue, but sadly, stupidly, it is.