How does the network apply credit for created blocks?
Miner has to supply the Bitcoin address for block reward. Then, when the block is mined, the special "credit" transaction is permanently stored in found block, creating given amount (25 BTC, was 50 BTC) to given address.

Some pools (Eligius or P2Pool) use this feature and create a lot of credit transactions, so that when block is found, all participants will receive their respective share.