Jim2007 example is right on the money, you don't know what is around the corner as anything from interest rates, employment statistics, quantitive easing, consumer confidence, etc etc will throw your investment into a roulette wheel. Don't forget it's a two horse race and not just a 'euro is no good' . You could make an effort of hedging your currency punt by not only a. choosing a currency that you believe to be safer but additionally b. choosing an index/stock in that currency and taking the view that while the currency may go up or down the stock/index could be worth backing I.e euro/usd is based on the past 12 months a good time to invest in s&p500 but again you're back on the racecourse.
There is a lot of speculation that ecb interest rates will come down with trichet gone and because of Europe being 'in a state of chassis' so you would imagine that euro will remain under pressure (of weakening), euro/usd has moved from. 1.34 up over 1.41 in the past week or so which is a big jump on the back of the Greek bailout but again sentiment seems to be that greece is f@$&ed so euro/usd may come back down. That could suggest that jumping into a non euro investment would make sense right now but again.....................too many variables out there for anyone to advise with any level of authority.