When is it bad for a currency to devalue?
Does this effect imports/exports somehow?
In fact it is generally very stimulative for an economy to have its currency devalue. So, unless the economy is in danger of inflation (and certainly Europe is more in danger of deflation than inflation at the moment), devaluation is all to the good.
As a happy side effect the US can also be more stimulative to try to competitively devalue as well.
Regarding imports/exports, obviously if you devalue your exports go up, as for imports, generally they will go down as they get more expensive, though this link is somewhat less direct.
Less direct? If anything it is more direct, I'd say. It's usually considered an important part of the stimulative effect since it makes people buy more domestically.
Devaluation is useless in the long run though.
