peer to peer.
When you are "downloading" the blockchain where do you think it is being "uploaded" from? The central Bitcoin, Inc server farm?

That being said the QT client is pretty horrible about bandwidth management. Since devs seem to have no interest in putting in speed caps you may want to look into a third party tool which will cap the speed.
Thanks for the replies. Well, I always thought that the miners served out the blockchain not the clients. And my client is behind a firewall, with no port forwarding, so how are other clients attaching to it?