I have seen similar comments elsewhere.

There have been previous lawsuits about whether the word "limited" is exceeded by previous extension acts. But this is the first to specifically attack the right of Congress to extend existing copyrights.

For more on the argument being used [link|http://eon.law.harvard.edu/openlaw/eldredvashcroft/supct/opening-brief.pdf|the brief] is surprisingly readable.

Cheers,
Ben