Editor and Publisher has the following on why the jury voted as they did:

He also said that they found Tim Russert of NBC “very credible” and the defense “badgering” Judy Miller may have hurt them as some jurors developed “sympathy” for her. Even though she admitted having a “bad memory,” the fact that she had notes counted a lot in her favor, he said.
Collins, a journalist who has written for The Washington Post and other newspapers, described the jury’s painstaking deliberations. He said there were several “managerial types” on the jury and they spent many days just assembling post-it notes in some kind or “buildings blocks” fashion. They did not take an immediately straw vote.
“What we came up with from that,” he said, “was that Libby was told about Mrs. Wilson [Valerie Plame] nine times” in that time period. “We believed he DID have a bad memory,” he said, “but it seemed vyer unlikely he would not remember about being told about Mrs. Wilson” so many times….Hard to believe he would remember on Tuesd and forget on Thursday,” and so on. [sic]

Here’s Byron York’s report on Russert’s testimony.