<font face="Verdana, Arial, Helvetica, sans-serif" size="2"> You make it sound as if you buy a new one each time...You know you can use the same Octopus card eternally...</font>
Each time I leave HK I turn in my Octopus card at the airport in order to get back my HKD50 deposit and because I had heard that the card's charged value (typically HKD 40 to 80) would expire after 6 months. Maybe I better ask them what the true interval is.