Some of us are following this closely on other sites, for example
www.dailykos.com has many threads up about this.
In a nutshell, Plame's status was covert (NOC), the present Director of CIA testified to that under oath on Friday, Plame herself did likewise. The information that she worked for CIA was classified: the identities of covert CIA case officers and agents are top secret.
NOC, Non-Official Cover, is the most highly secret status within CIA, because these are Americans who do not have diplomatic immunity overseas: they can be arrested, tortured, and executed by foreign governments.
The fact that she did rotations back to Langley don't change that, any more than a General is not still a General when he's rotated out of a combat zone.
Whoever initiated that leak is liable for at least a felony violation of the Agent Identities act, and since it occurred during wartime in a region of conflict, charges of treason could also be brought.
Bush claimed he would get to the bottom of this and see to it that whoever was involved would be fired and prosecuted fully.
We are still waiting.
And yes, there are almost certainly impeachable offenses involved, even if one doesn't count the treason charge.
Meanwhile it looks as if Alberto Torquemada might get thrown under the bus this week over the Federal Attorney scandal.