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Why write about the yen/dollar or yen/Euro relationship?
Because I'm American (and I like the Europeans a lot, too). No, really. For the US and Europe, the relative values of currencies not only determine what we pay for our camera equipment, but also impact the profit that the Japanese companies make. While I try to avoid political discussion on this site, the US government's policy of letting the dollar stay weak against other currencies to try to encourage US exports definitely had impact on all of us. Nikon, for example, in their 2011 fiscal year reported that the appreciation of the yen (against both the dollar and Euro) had a net impact of -27 billion yen in their profits.
If you build something but by the time it actually sells overseas it brings in 5% less than you expected due to currency fluctuation, your gross operating profits go down. Meanwhile, for those of us at the other end, eventually our local subsidiaries of Nikon have to raise prices. As I write this (3/13) the yen/dollar relationship has reversed and is now trending towards a constantly depreciating yen. Overall, we photographers want a stable yen/dollar or yen/Euro relationship, as it means the companies we count on continue to be profitable and the prices we pay for our equipment don't change or get out of hand.
So, if you're trying to figure out how things are going, look up the current currency rates and compare them to these: 90 yen to the dollar, 120 yen to the Euro. Those are the figures that Nikon is currently (early 2013) using to predict prices and profits. If those numbers go down significantly (say 80 yen to the dollar or 105 yen to the Euro), we'll see price increases. If those numbers go up significantly, we'll see more frequent rebates and more sales of camera equipment.