The person who disclosed Valerie Plame's name was Richard Armitage, not Libby.
It is indisputable that Armitage spoke Plame's name in connection with her husband to a media figure - Robert Novak.
The investigation was to find out who, if anyone, instigated Armitage to talk to Novak and to get that story in print. The theory that was not proved, but suggested, was that the Vice President's office (who was running the operation to sell the Iraqi War to the public and Congress, while State had the job of convincing allies and the UN) had dispatched Libby, who had gotten his associates to start shopping the story to friendly media sources, anonymously. This is why many other media figures were called to testify.
Chief of State for Vice President Cheney, Scooter Libby has four meetings with the New York Time's Judith Miller, where he reveals Plame's role in getting Wilson sent to Niger, and claims that the uranium finding was a key element of the official intelligence case against Iraq. This was false. By suggesting this to her, he was saying that Wilson's findings were discarded, when in fact, his findings from his Niger trip caused the yellowcake allegations to be removed from the official intelligence estimates.
Libby claimed that he didn't know Plame was an agent of the CIA, undercover or not, but that he learned it from Tim Russert. Russert refused to testify about any conversations between Libby and himself, but it turned out at trial that Russert did immediately tell FBI agents investigating the leak that he not spoken with Libby about Plame. Libby actually heard that Ms. Plame was part of the CIA's counter-proliferation team directly in a phone conversation with Vice President Cheney. Immediately after that, it is now known that Libby also heard the same information from an Undersecretary of State, Marc Grossman. About a month later, Libby tells White House Spokesperson Ari Flescher that Wilson's wife was a CIA asset and had arranged his trip to Niger. Shortly after that, Libby then tells that information to Robert Novak, but without using her name. Novak looks up Wilson in Who's who, gets her name that way. White House Chief of Staff Karl Rove calls Novak, and discloses that he heard, from another unknown journalist, that Plame was a CIA operative.
The same day that Novak's article was published, another journalist, Matt Cooper from Time, is called by Karl Rove, and told not to "get too far out on Wilson", and that his trip to Niger was not approved by the administration, or any highs up at the CIA, but rather, by Ms. Plame, and that there was still plenty of time to implicate Iraq in getting yellowcake from Niger.
One day later, another journalist, Walter Pincus, was told by an unnamed White House source that Mr. Wilson's work was not authorized by the CIA, that it was his wife who sent him, and that the trip was a "boondoggle". The same day that this happened, Pincus was in a "reporting gaggle" that was held by Flescher, on his last day as spokesman, where it was revealed that Flescher also reported that Wilson was sent to Niger by his wife, who was an employee of the CIA.
Two days after the original article by Novak, another article, this time citing two White House officials, re-states that Wilson's wife was a CIA employee and that Wilson's trip was prompted by his wife.
From here, it's pretty clear three things:
1. There was a concerted plan to get Wilson discredited by using friendly journalists. There are at least 4 well-known journalists - Novak, Miller, Cooper and Pincus, who all report that contacts in the White House and State Department told them that Plame was a CIA employee and insinuated that Wilson was sent to Niger at the behest of Plame, and this trip and the related findings were not reliable.
2. This information was factually untrue, Wilsons' trip and it's report led the CIA to strike the yellowcake claims from it's official intelligence estimates. The State Department resisted this report, and pursued it's own version events. White House and State department officials lied to journalists about the value of Wilson's report, and used those lies to instigate anonymously sourced stories in the press discrediting Wilson by using his connection to the CIA through his wife, Plame. The White House ignored the fact that CIA did value Wilson's report, but used an also discredited report from Great Britian to support the claim that yellowcake was obtained via Niger.
3. The only reason that more people did not go to jail - including Rove, Armitage, and Novak is it cannot be proven that any of them knew that Plame was an identity protected person. Because of this, they did not knowingly break the law that protects undercover agents identities. Libby, on the other hand, flatly lied and told the FBI and grand-jury that he had heard Plame's name from Russert. At this point, he had already revealed the name to Judith Miller. Miller refused to testify about this for some time, but as soon as she did, it was the smoking gun that he obviously knew Plame's name before he heard it from Russert. During the trial two more bits of information came out - that Cheney and an Undersecrtary from State also told Libby Plame's name. The only reason Libby isn't doing serious time is that no one specifically testified that Libby was told that Plame had a protected identity. Although it was disclosed she worked on nuclear issues for the CIA, it was never shown that Libby (or any of the other known leakers - namely Rove, Armitage, or the unnamed offical who spoke to Pincus) knew Plame was a protected agent.
There is no doubt that there was a co-ordinated effort to discredit Wilson's report. There is no doubt that multiple White House and State department officials knew the information and passed it along.
The difference between what just happened in Afghanistan and what happened with the Wilson/Plame affair is that the recent event was very likely an honest mistake. The person who made the mistake did not have an intent to discredit the CIA operative. He was not grinding an axe for producing intelligence that the Administration disagreed with. If those assumptions are false, we have a good equivalence. In the Wilson/Plame affair, there was quite obviously a co-ordinated and well-documented campaign to punish Wilson and by association, Plame, for having a contrary voice. Epsecially while this was happening it was blowing up in the administration's face that there were no weapons of mass destruction in Iraq that we didn't already know about.
I have more sympathy towards Rove, Libby, and others because it turns out that Novak called another government source to confirm Plame's identity, and this source correctly did not reveal the name or confirm that she was covert (because confirming it would be to reveal classified information). This leads me to believe that it was routine to think of CIA employees as just government workers, and not covert agents, and that within the CIA there was no obvious and great barrier between career employees and covert agents. Plame basically moved between assignments that had covert and non-covert cover depending on what phase her career was in. When some knew of Plame's covert nature, it was protected, and it was likely that everyone in the administration knew not to intentionally release that type of information. This is effectively why the special prosecutor did not bring more charges - there was no evidence that anyone who leaked knew that they were leaking classified information. Instead, they viewed it as just regular run of the mill political gamesmanship, or as Rove was quoted as saying, "fair game". To me this is despicable, but Fitzgerald probably made the right call not to prosecute on more serious charges because of a lack of clear intent to reveal classified information.