If you trade with bitcoins, how do you manage to "explain" anti-laundering authorities the money-in & money-out? When trading with bitcoins using mtgox, or bitcoin-24, or bitcoin.de, you will have in your account many transfers of money, to many people and from many people. In europe if the sum of the transactions is more than 10.000 €, your bank should send a notice to anty-laundering authorities.

How do you manage it?
I think your premise is flawed - when trading on Mtgox or other exchanges, there will only be transfers between you and Mtgox. If you're a day trader most trades will be internal on Mtgox and not be settled by the banks at all.

Even if they do "send a notice to anti-laundering authorities", it doesn't mean the next day they will show up at your doorstep to arrest you, it just means those authorities are aware of the transactions, and if they detect a suspicious pattern they may ask you questions. In this case you can just tell the truth.