Exposing an agent is a felony, and a severe enough one that Bush I -- a former head of the CIA -- once said, "I have nothing but contempt and anger for those who betray the trust by exposing the name of our sources. They are, in my view, the most insidious of traitors." Not only does it mean that this operative can never do any work ever again, it also means that any contacts she cultivated over the last decade or two probably have to be written off, and may well be in personal peril.
People for the American Way has a petition to appoint an independent counsel to investigate the leak. I expect others will follow suit.
The administration's conduct on this matter is so reprehensible that President Richard Nixon's Watergate-era aide, John Dean, was moved to write: "If I thought I had seen dirty political tricks as nasty and vile as they could get at the Nixon White House, I was wrong... Nixon never set up a hit on one of his enemies' wives."
I don't think anything will come of this -- the administration and Congressional majority will probably try to avoid ever letting the guilty party be caught, esp since it looks like Karl "Bush's Brain" Rove may be implicated in some way. (Rove, incidentally, was fired in '92 by Bush I's campaign, allegedly for vindictive leaking to the same Robert Novak.) Nonetheless, I plan to write up a fax to my congress-critters encouraging them to make noise about the issue. Any of you who have Republican congress-critters are strongly encouraged to follow suit.
ETA: Slate summary. I still think the leak should be taken more seriously than Shafer is giving credit for, because of the revenge / intimidation aspect, and the recklessness of the whole thing. (It is Not OK for high-ranking government officials to think they can get away with breaking, or at least bending, this sort of law, in the pursuit of political vendettas.)