“We launched an exciting feature today: off blockchain micro-transactions between Coinbase accounts! Here is a bitcoin transaction I just sent myself for 1 satoshi (that is 0.00000001 Bitcoin). The transaction arrived instantly, confirmed instantly, and cost zero in fees. This was possible because it did not touch the ‘blockchain’ (the public ledger of all bitcoin transactions), and instead was sent directly between two Coinbase accounts.”
http://blog.coinbase.com/post/57483182558/you-can-now-send-micro-transactions-with-zero-fees
