Don't get me wrong. Perjury is a crime for a reason. It's especially heinous when committed by high government officials.
If it turns out Libby was covering his own ass on purpose, to the detriment of the investigation, then he's right where he should be right now. And can I take a moment to point out that, just as Bush promised, the first person to be formally accused of anything was immediately removed from the administration?
On the other hand, while the prosecutor and the Grand Jury believe there were shenanigans here, the accusation of perjury still needs to be proven to a jury in a proper trial. It may be that, based on the evidence, the trial jury will conclude that Libby made an honest mistake and that no perjury actually occurred.
And this, after two years of investigation, is the most terrible thing the administration may have done regarding Valerie Plame: possibly on purpose not remember the exact details of how one staff member didn't actually do anything wrong. Possibly.