Overall it's massive news and a great prospect for the long term viability. Short term it might spook some day trading types for no particularly convincing reason.
obviously you don't understand how coinbase works. they are a exchange but also the counterparty to every trade. so coinbase buys the BTC and then sells it to it's customers for a markup. they don't buy unless they already have a seller lined up. it's almost risk free for them and sucks if you are selling BTC, but hell, at least they send you your USD in a week. still waiting on a wire xfer from gox I initiated November 11.