yes, you can buy it now. as it will be appreciated again after OBAMA's economic team dealed with their problem, but it takes sometimes (some economists said 2-3 months). If you are not planing to use your Yen at these moment, you can buy and stock it. Be careful! keep it in the safe place lolz
Too bad, IMF just announced that next year economy will be deepen and telling all government should be prepared for next bumping ride in the year 2009. So, if no need to use yen for at least a year, then u can buy US. Anyway, enjoy what you have and earn!!