...And if the memo was a plant by conservatives, why is CBS hiding the source?
You don't expect their investigative and analytical skills to go *that* far, do you?
My guess is that the more plausible conspiracy angle will be this: that the White House came in possession of the documents (my understanding is that they had been given them by CBS so that the WH would grant permission for their release) and after examining the documents the WH realized there were significant problems with them and that they were likely fakes. But they didn't bother saying anything about it. Why should they? Instead, as the conspiracy theory would go, they decided to wait and let doubts be raised via the internet once the 60 Minutes show aired (in this case through a certain Freeper going by the name Buckhead).
Plausible? To be honest, i think it is. And if it did happen this way, i say good for the WH and i also say that CBS got what was coming to them. CBS were the ones with the responsibility to check out the documents and verify them. Not the WH. And by not checking them out in a thorough manner (or more to the point by ignoring doubts raised by their own experts) they deserve to be humiliated and exposed as the Republican hating organization that they are.