The yen has appreciated by around 50% against the US dollar since the end of 2006 so the yen price of the lens is roughly unchanged over the period. The question now is what might happen to the USD price if the dollar reverses some of its depreciation.
Yes, the dollar/yen exchange rate is horrible now, worst in history.
It is about $1 = 77 yen. I have been coming to Japan since 1985 and lived in Japan several times so I am always following the exchange rate. We had a nice spike in 2007 when I was here for 3 months and it was $1 = 120 yen, but since has dropped dramatically. My timing for that 3 months was wonderful! I recall that for a short period in 1995 when I was here it got down to $1 = 79 yen for a day or two, but then soon started moving back up. I would be comfortable if it was in the $1 = 100 yen range (which is probably a reasonable average for the last few years) because then prices for many things are more inline with U.S. prices. We are back in Japan now and probably will be for awhile, but the terrible exchange rate means everything costs a lot.
Checking a bit on camera gear recently I saw that with a 100 yen exchange rate prices would be pretty similar to the U.S. for most things, but with the 77 yen exchange rate it makes most stuff very expensive. I do recall a week or so ago seeing a couple of cameras though that even with the terrible exchange rate the prices were lower in dollars than in the U.S. I don't recall what they were, but I was browsing kakaku.com and saw them.
Recently I have read a couple of times predictions that in 2012 the dollar will probably get stronger. I sure hope so -- as long as it doesn't hurt stock prices too much.