A number of readers misunderstood my explanation of Rav Ettlinger's question regarding esrogim from the other side of the world, and looking back at how I explained it, I see that I did not use the right words. Rav Ettlinger did not view the world in the same way as, say, Rav Moshe Taku, who held that the heavens (and God) are vertically above us and not also on the other side of the earth. Rav Ettlinger was well aware that there is no absolute frame of reference. Indeed, in formulating his question, he himself says that the same question applies the other way around - i.e. that Jews in Australia who import arba minim from Israel might have to turn them upside-down relative to them.
But in my view (and apparently some disagree), this sort of question would not be asked today. It would be inconceivable to us to be concerned about the position of the tree in Australia relative to Israel, and vice-versa. I doubt that even the most fervent Brisker would also make sure to hold arba minim imported from such countries upside-down in order to fulfill his obligation (but then, I am often surprised by people). This question was only asked by Rav Ettlinger because people at that time were still in the process of internalizing the knowledge of the shape of the world. He had to explain why Australians don't fall off the bottom of the world by invoking gravity; today, it is "obvious" that there is nowhere to fall to, and nobody would have to explain it. And my point was this does not reflect any foolishness on his part; even we today have still not entirely internalized the correct view, and we feel uncomfortable with an "upside-down" map of the world.
By the way, I was led to this discussion by reader Yaakov Yehudah who attended (and arranged) a presentation that I gave this week on the subject of exotic shofars. In the lecture, I raised the question of whether the requirement of holding an item derech gedelaso also applies to shofar, which would have very strange results when applied to a shofar from a kudu - one would have to hold it upside-down from the position in which it is normally held. If you would like to attend this presentation, I am giving it online on Sunday via live video feed - you can sign up at http://torahinmotion.org/virtproglib/e-tim/index.htm. The software allows for participants to also IM their questions during the shiur, and even to speak up and be seen if they have a webcam. This is basically the same material from my essay that can be freely downloaded at http://www.zootorah.com/essays/ExoticShofars.pdf, but in the live presentation I will be showing some additional artifacts.