Confession: I always assumed (until EY's article, believe it or not!) that the "tree falling in a forest ..." philosophical dilemma was asking whether the tree makes vibrations.

That is, I thought the issue it's trying to address is, "If nothing is around to verify the vibrations, how do you know the vibrations really happen in that circumstance? What keeps you from believing that whenever nobody's around [nor e.g. any sensor], the vibrations just don't happen?"

(In yet other words, a question about belief in the implied invisible, or inaudible as the case may be.)

Over what period, exactly, was the question widely accepted to be making a point about the difference between vibrations and auditory experiences, as Eliezer seemed to imply is the common understanding?

The "tree falling in a forest" question was posed before people knew that sound was caused by vibrations, or even that sound was a physical phenomenon.

I don't think that's correct. The notion that sound is vibrations in air dates back to at least Aristotle. See for example here

Do you have a citation for that? The earliest reference I see is Berkeley.

That's not quite what I meant either (although I actually approve of avoiding the term "qualia", full stop):

To categorize is to throw away information. If you're told that a falling tree makes a "sound", you don't know what the actual sound is; you haven't actually heard the tree falling. If a coin lands "heads", you don't know its radial orientation. A blue egg-shaped thing may be a "blegg", but what if the exact egg shape varies, or the exact shade of blue? You want to use categories to throw away irrelevant information, to sift gold from dust, but often the standard categorization ends up throwing out relevant information too. And when you end up in that sort of mental trouble, the first and most obvious solution is to play Taboo.

For example: "Play Taboo" is itself a leaky generalization. Hasbro's version is not the rationalist version; they only list five additional banned words on the card, and that's not nearly enough coverage to exclude thinking in familiar old words. What rationalists do would count as playing Taboo - it would match against the "play Taboo" concept - but not everything that counts as playing Taboo works to force original seeing. If you just think "play Taboo to force original seeing", you'll start thinking that anything that counts as playing Taboo must count as original seeing.

The rationalist version isn't a game, which means that you can't win by trying to be clever and stretching the rules. You have to play Taboo with a voluntary handicap: Stop yourself from using synonyms that aren't on the card. You also have to stop yourself from inventing a new simple word or phrase that functions as an equivalent mental handle to the old one. You are trying to zoom in on your map, not rename the cities; dereference the pointer, not allocate a new pointer; see the events as they happen, not rewrite the cliche in a different wording. [emphasis added]

By visualizing the problem in more detail, you can see the lost purpose: Exactly what do you do when you "play Taboo"? What purpose does each and every part serve?

The specific advantage I see of cracking open the black-box of "consciousness" in this conversation is that I expect it to be the fastest way to one of the following useful outcomes:

1. "But you haven't talked about fribblety chacocoa opoloba." "I haven't talked about what? I don't think I've ever actually observed that."

2. "On page 8675309 of I Wrote "Consciousness Explained" Twenty Years Ago Haven't You Gotten It By Now by Daniel Dennett, he says that fribblety chacocoa opoloba doesn't exist - here's the quote." "Oh, I see the confusion! No, he's talking about albittiver rikvotil, as you can see from this context, that quote, and this journal paper."

3. "On page 8675309 of I Wrote "Consciousness Explained" Twenty Years Ago Haven't You Gotten It By Now by Daniel Dennett, he says that fribblety chacocoa opoloba doesn't exist - here's the quote." "But that doesn't exist, according to the four experiments described in these three research papers, and doesn't have to exist by this philosophical argument."

Edit: Also, there's no requirement that you actually solve the problem of what it is - a sufficiently specific and detailed map leading to the thing to be observed suffices.