grammar - None have showed up? Huh?

This is a silly shibboleth brought to you by hyper-corrective grammar pedants. Here is a usage note that explains it in simple terms:

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 n, "one," but the word has been used as both a singular and a plural noun from Old English onward. The plural usage appears in the King James Bible as well as the works of John Dryden and Edmund Burke and is widespread in the works of respectable writers today. Of course, the singular usage is perfectly acceptable. The choice between a singular or plural verb depends on the desired effect. Both options are acceptable in this sentence: 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.

All my paper dictionaries (OED, Wester's Third New Int'l, etc.) agree on this point. None takes both a singular and plural complement, depending on the circumstances.