A three-judge panel on the 11th Circuit Court of Appeals concluded that the individual mandate exceeded congressional authority under Article I of the Constitution because it was not enacted pursuant to Congress's tax power and it exceeded Congress' power under the Commerce Clause and the Necessary and Proper Clause.  It was a split decision, with one judge dissenting.

This, of course, means that there is a split in the circuits, given the Sixth Circuit ruled that Obamacare is constitutional.  Clearly (and as everyone predicted) this is going to the Supreme Court.

The dissent in the 11th Circuit (by a Clinton appointee, but a Republican) is pretty scathing. "Quite simply, the majority would presume to sit as a superlegislature, offering ways in which Congress could have legislated more efficaciously or more narrowly," he wrote. "This approach ignores the wide regulatory latitude afforded to Congress, under its Commerce Clause power, to address what in its view are substantial problems, and it misapprehends the role of a reviewing court. As nonelected judicial officers, we are not afforded the opportunity to rewrite statutes we don't like, or to craft a legislative response more sharply than the legislative branch of government has chosen."

The opinion and dissent are below.

UPDATE:  It appears (from my cursory review) that the 11th Circuit would sever the individual mandate from the rest of Obamacare, which it finds to be okay constitutionally. 

Florida et al v. Dept. Of Health & Human Services et al