Yesterday evening's Word Court by Barbara Wallraff in the local paper leads with a "simple rule" about the use of a and an: "If you hear the 'h', use 'a'." It always cracks me up to people who take themselves seriously say "an historical event". It's a nice example of how screwed up prescription can get. Wallraff unfortunately doesn't say anything about the history beyond "historically, not everyone did pronounce its 'h'", which is a shame. Most people reading her column don't know anything about the history of our indefinite article, nor about the reanalyses involving moving an n, etc. Sigh. People would find that much cooler, than the little and obvious lesson.
But I'm wondering about the continuation of the reduction of the indefinite article: I hear speakers use a when the following words begin with a vowel. In part, it's obvious rapid speech reduction, and speaker of some varieties (Southern) seem to do it a lot, but I suspect it's creeping along. That makes an historical even more of a stupid scrimmage fought as we retreat from old forms.