Actually, Jose Padilla, an American citizen, was picked up shortly after 9/11 at the Chicago Airport, labeled an enemy combatant, and incarcerated without access to an attorney for over 2 years in a military brig (although not Guantanamo, but frankly, the location doesn't matter much).
After pressure from recent Supreme Court rulings, his case was turned over to civilian courts just last year. The government's key witness in the case was a rival drug dealer from over a decade ago (a former drug dealer, Padilla exhibited no criminal behavior for over a decade before his detention). This key witness has since RECANTED his testimony. Most legal experts agree that, because of this, the government will likely lose it's case and have to set Mr. Padilla free. If he doesn't plea bargain to gain his own release, that is.
So, yes, American citizens have much to worry about.
Anything else, Brick?