The full block download and verification isn't needed to start hashing the next block?
The idea is to only submit the transaction hashes which go into the merkel tree, instead of the transaction data. Because it is likely that you already received and validated the transaction, before you receive a block containing it. This technique removes redundancy from the communication between the node and the network and significantly reduces the time to propagate a valid block.
But is not currently how the Satoshi client operates, right? I know we don't have too many people running stock software and huge pools.