(from http://www.bitcoin.org/smf/index.php?topic=1872.0)

Allow extra parameters to be attached to an address/account at creation and modified later:

• $uri: JSON-RPC callback URI
• $total: Transaction total in BTC
• $timeout: Transaction expiration interval (sec)
• $minconf: Transaction minimum confirmations required
• $cert: PEM certificate for callback target server

Additional options passed in should also cover these use cases:

Fire $uri, including parameters for the current balance and the most recent payment received, when:

• Any payment is received to the address/account with $minconf confirmations.
• Balance on address/account >= $total with $minconf confirmations.
• $timeout expires without balance on address/account >= $total and without at least $minconf confirmations.

With this, bitcoind is ready to become a fully-fledged payment back-end for internet commerce.