Never use an exchange address as username on P2Pool!  You will not receive your coins.  Not only does Cryptsy warn you not to do this, BlackGold says on their homepage too: "Don't use an exchange address!".    P2Pool doesn't send the coins, it mines them.  And the exchange is unable to determine who mined them.  Just look at the transactions list in your own wallet.  Notice that the 'mined' coins have no address associated?  Well the exchange would see the same thing, incoming mined coins with no way to know who mined them.