It's an idea that has been proposed by a number of science fiction authors, including Heinlein. They've generally predicted the secession of Washington, Oregon, and sometimes California, as a rebellion against increasing authoritarianism. The Republican mishandling of California's economy, and the rise of neo-conservativism, might lend a little credence to such predictions. On eithnic lines, the Southwest is probably the moslt likely candidate. I don't think it's likely that it will happen soon, but 20 years from now? If the Neo-Con dynasty gets its way in the next couple sets of elections, who knows what could happen?