I have a little problem which I ignore because it is just an inconvenience. Every 10 shots or so I get very slow writing speed only because there is a SD card in the second slot. I am NOT writing to this card but it is there just in case I forget CF cards at home (happened before). So, at CES I talked to Nikon rep who supposedly is in service department. I was told that because SD card is part of the bus now it does not matter if I am writing to it or not. It slows down the whole bus. Except it does not happen every shot. And it happens randomly. He suggested to use the same speed SD card as CF card but I don't have 400x SD cards.