likely deepbit or slushes pool or one of the exchanges no?
pools pay the miner, so i think it's so hard they can have 300k, dunno mtgox volume at moment btw we're talking about a single address..
most mining pools take a percentage (2-3%), with pools like deepbit solving a block every 2-20min currently (average of 17minutes per block at the moment) (months ago it would have been way way way easier) thats 1.5btc every few minutes to them.. or maybe i'm misunderstanding their cut?
https://deepbit.net/statsby the looks of that they are making a couple hundred btc every day from the fee they are charging