This closes the debate...

None can be used in formal writing with either a singular or a plural verb depending on context. This topic has been amply discussed in the following usage note from American Heritage Dictionary.

Usage Note: It is widely asserted that none is equivalent to no one, and hence requires a singular verb and singular pronoun: None of the prisoners was given his soup. It is true that none is etymologically derived from the Old English word ân, "one," but the word has been used as both a singular and a plural noun from Old English onward. The plural use can be found in reputable sources such as the King James Bible, Dryden, and Burke; and H.W. Fowler described the traditional rule as "a mistake." Either a singular or a plural verb is acceptably used in a sentence such as None of the conspirators has (or have) been brought to trial. When none is modified by almost, however, it is difficult to avoid treating the word as a plural: Almost none of the officials were (not was) interviewed by the committee. None can only be plural in its use in sentences such as None but his most loyal supporters believe (not believes) his story.



Excerpted from The American Heritage® Dictionary of the English Language, Third Edition © 1996 by Houghton Mifflin Company.