I have been keeping a pretty close eye on the dollar. I am very worried about it myself at the moment (though it will help out for my fiance to transfer her money to dollars.) I have been looking for a bottom...and I don't think that has happened yet.
However, from my experience exchange rates in America are significantly worse than those in Japan. I remember multiple occasions where both the local banks and the airports were offering 99-103 yen per dollar whereas the airport in Japan was offering 122 yen per dollar at the exact same time.
You may know of a great fair place to exchange money in the states, but I do not.
Consequently, my experience says you would be better to wait until you get to Japan to make the exchange, even if the dollar were to lose a few more points on the yen by then.
Personally, I would move my money into the Euro. It is unlikely to drop at all and several oil companies are discussing the possibility of switching from the dollar to the Euro which certainly won't hurt the Euro any. Then if the yen goes down or the Euro goes up you can switch your money over when you get to Japan for a fair rate and hopefully make up a little bit of what will be lost at the moment, but at the very least you wouldn't have to worry about any major drops.
