"She hasn't said but a few words to me since last winter."
"She has said but a few words to me since last winter."
Which of these is right?
I think the latter is heard more often, but the former makes more sense to me. It's saying that she hasn't said anything to me except a few words since last winter, whereas I can't break down the second in a similar fashion.
I can also think of sentences constructed in a similar fashion to the second sentence that are in common usage, such as, "I have but one request to make." This doesn't make sense to me, except to the extent that it is idiomatic or uses "but" in a different sense (e.g. "only"?), and I suspect that this is idiomatic. Using "but" with a negative, however, makes more sense to me, if we use it to mean "except".
Quite possibly, I could be wrong in everything I've said above.