http://www.law.cornell.edu/supremecourt/text/408/665 Branzburg v. Hayes
That case also says this:
The administration of a constitutional newsman's privilege [p704] would present practical and conceptual difficulties of a high order. Sooner or later, it would be necessary to define those categories of newsmen who qualified for the privilege, a questionable procedure in light of the traditional doctrine that liberty of the press is the right of the lonely pamphleteer who uses carbon paper or a mimeograph just as much as of the large metropolitan publisher who utilizes the latest photocomposition methods.
The efforts now underway to create a federal "shield law" would gut the first amendment. It would be a license to publish
A passing thought:
That statement about the liberty of the press with respect to the little guy versus the big guy would lead me to think it correlates to today’s bloggers versus the mainstream media.