The best way to make it unlikely to happen is not to charge the tablet using the USB port. This means to charge the batteries using an external charger, which I would guess mean much less usage of the port -- you only need to use it when you would be flashing or transferring data directly. Most heavy users of the N900 recharge every day or two, or hundreds of times a year, I would say.

Every use of that port makes it more likely that the problem will occur.