Depends what you want to do with the money. Personally, I set up a Dollars currency account just to host my AdSense cheques. Kindly, Google does not do electronic funds transfer to a currency account so I have to stick with long waits and delays.
With the Dollars not being exchanged, I'm building up a travel fund and not losing value (apart from US inflation). I go to the USA once in a while, and the earnings pay for pretty much everything I do there. World-wide, there are a few currencies pegged to the US$, so the money can be used for traveling to those countries too.
In short, you'll only have a problem if you want to use the earnings in Europe. Otherwise, you can be very creative with it.
A related note: I sometimes wish Paypal would let me link my US$ account to my Paypal account. That would make life so much easier.
One thing I forgot to mention in my original reply: if you keep the US$ as is, maybe you can use them to pay for online services like hosting and stuff. It would be neat if you could like a currency credit card to help that along.
With the Dollars not being exchanged, I'm building up a travel fund and not losing value (apart from US inflation). I go to the USA once in a while, and the earnings pay for pretty much everything I do there. World-wide, there are a few currencies pegged to the US$, so the money can be used for traveling to those countries too.
In short, you'll only have a problem if you want to use the earnings in Europe. Otherwise, you can be very creative with it.
A related note: I sometimes wish Paypal would let me link my US$ account to my Paypal account. That would make life so much easier.
Pierre