Well, certainly slander is a limit.
But, that is it.
Anonymous sources are vital to journalism.
Without them, many corrupt govt. officials would never get revealed.
Does the press abuse them? Yes. But, that doesn't mean they should have their press freedom taken away.
Now, as for the Plame case, it will be interesting to see who the leaker is. I don't think this will be some horrible end-of-the-world scenario to have this source divulged in this relatively unimportant case.
But, it could stifle the ability in the future to get anonymos sources in stories that are vital and need them because people are afraid of retribution for talking.
I do not agree that slander is (or should be) the only limit.
1) There is no First Amendment reporter's privilege; the privilege is not Constitutionally mandatory. This was, in fact, already well-established by Supreme Court precedent, and was presumably raised by Miller and Cooper in hopes that if the appeal reached the Supreme Court, the Court might overrule its earlier holding, but the SCOTUS holding was clearly binding on the Circuit Court.
2) There may or may not be a federal common law reporter's privilege (there was no majority on either side of this question).
3) Even if there is a federal common law reporter's privilege, it does not apply to the facts in Miller's and Cooper's cases because their is no other way to obtain the information sought.
There seems to be some confusion about the issue from the Appeals Court because Sentelle wrote two opinions, one for the whole panel of the Court which is the Court's decision in the case and one for himself as a separate concurrence. It was in his concurrence that he argued that there was no federal common law reporter's privilege, but that was his individual opinion, not the holding of the Circuit Court. Justice Tatel, in his concurrence, took the opposite tack, that there was a privilege but it did not apply as set forth above.
I'm not buying it. I am seeing that excuse used to disseminate flat out lies, though.