I think Grant's dismissal of "an historic event" as "simply wrong" is misguided. First, let us dismiss Martha's objection that no one would say "an hippie"–of course no one would, and no one ever suggested it. "An" occurs in this optional case only with words beginning with H _on an unstressed syllable_, where, as Grant points out, the H sound is often elided in many dialects. A horrible drive led to an horrific accident. The N in this case serves to separate two vowels that would otherwise become an unclear glide or diphthong.

But even in dialects where the H is pronounced, the English H is a rather weak and breathy thing–not at all like the fricative consonant sounds of the Spanish J or German CH. In this case, "a historic" requires either a conscious strong exhalation or a weak glottal stop to separate the vowels, both of which feel awkward to my mouth. Otherwise, the words sound like "astoric".

So personally, I use the optional "an" on such words, because it sounds clearer and feels quite natural to me in speaking. And I see no reason not to write the actual words I say, so if I say that a hero performs an heroic act, I will also write it.