Sioux Indian reservations covering 5 states and joined together as the Lakota Nation and have suceeded from the U.S.. They say it's completely legal. I just hope they planned well for the "now what moments" and I hope they put their message as video on video sharing sites.

This quote is from their website--
"During the week of December 17-19, 2007, we traveled to Washington DC and withdrew from the constitutionally mandated treaties to become a free and independent country. We are alerting the Family of Nations we have now reassumed our freedom and independence with the backing of Natural, International, and United States law."

Read about the sucession from Lakota Freedom or Google "Lakota Freedom" to read press stories.