When your friends don't call anymore, you haven't shaved for a month and there isn't even enough food in the house to make salad cream and cornflake sandwiches; yes, then that is the time to stop.
As for Flash memory, isn't the specification like 100,000 writes before it starts to go bad? If you flash once every 5 minutes it would take you... a very long time before your Zaurus memory failed. Even then the memory controller might detect the bad area and stop using it, allowing you to continue.