Talk Left discusses the latest Plame information which is interesting. I want to focus in on this part:

Finally, the new information once again highlights the importance of
the testimony of journalists in uncovering whether anyone might have broken the
law by disclosing classified information regarding Plame. That is because both
Rove and I. Lewis (Scooter) Libby, the chief of staff to Vice President Dick
Cheney—who are at the center of the Plame investigation—have said that they did
not learn of Plame's employment with the CIA from classified government
information, but rather journalists; without the testimony of journalists,
prosecutors have been unable to get to the bottom of the matter.

Certainly part of this investigation is what did Rove/Libby tell
journalists. That is, were they the leakers? This is where the "journalist
protecting source" stuff comes in.

The other part of this now is, obviously, "what did journalists tell
Rove/Libby?" I know I'm just a blogger with limited ethics, but I have no idea
how this falls under any kind of source protection concept. It'd be one thing if
it were some double super secret that Rove and Libby ever talked to the press.
That is, if they were genuine whistleblowers such that the very fact that they
talked to the press at all was secret. But apparently part of their testimony
involves admitting they talked to journalists and claiming those journalists
told them that Plame was a CIA op.This falls under source confidentiality
protection how? I can't think of any reason that Judith Miller shouldn't answer
the following question:

Did you inform Karl Rove or Scooter Libby that Joe Wilson's wife was a
CIA operative?

There's no source confidentialy issue there at all, not even in the fevered
imagination of Bill Keller.