If you're intrigued by Grigory Perelman, the man who proved the Poincaré Conjecture and a new hero to refusiniks everywhere for declining the Fields Prize and the million-dollar Millennium Prize, this profile by Sylvia Nasar and David Gruber sheds some light. There are a lot of indifferently introduced characters in the story, and if you have any idea what it means that "manifolds of the fourth, fifth, and higher dimensions were more tractable than those of the third dimension," you're welcome to try it out in the comments. (I say it's still a sphere, and I say the hell with it.) But it's a pretty good portrait of flaming eggheads. Perelman comes off as less of an eccentric than he has in most of the spot news coverage of his solution. The short answer for why he's saying no to the award (while keeping his options open about the million) is surprisingly sensible:
Perelman repeatedly said that he had retired from the mathematics community and no longer considered himself a professional mathematician. He mentioned a dispute that he had had years earlier with a collaborator over how to credit the author of a particular proof, and said that he was dismayed by the discipline's lax ethics. "It is not people who break ethical standards who are regarded as aliens," he said. "It is people like me who are isolated… Of course, there are many mathematicians who are more or less honest. But almost all of them are conformists. They are more or less honest, but they tolerate those who are not honest."
The prospect of being awarded a Fields Medal had forced him to make a complete break with his profession. "As long as I was not conspicuous, I had a choice," Perelman explained. "Either to make some ugly thing"—a fuss about the math community's lack of integrity—"or, if I didn't do this kind of thing, to be treated as a pet. Now, when I become a very conspicuous person, I cannot stay a pet and say nothing. That is why I had to quit."