In his review of the new film Fair Game, an odious pack of lies about the Plame affair, Roger Ebert says this:

In the film, we see that Plame, under a variety of aliases, ran secret networks of informants in Bagdad and other Middle Eastern cities. When the administration blew her cover, several of her informants were killed; some reports say 70. Then the Bush spin doctors leaked the story that she was only a CIA "secretary."

I have no idea what left-wing fever swamp Ebert pulled that information from. But I think I'll take the word of the 34-year CIA veteran tasked with reporting on the damage from the Plame affair that there was likely no harm done by leaking her identity.