look at mac user experience
with usb hdd backup on leopard 10.5
There is a massive bug in the USB drivers for external drives that will cause data loss. If you are using an external USB drive for storing any important data, disconnect it from any Leopard (10.5.1) systems that you have, and don't use it until you know this bug has been fixed. Note that this also applies to any USB-based hardware, such as a camera.
so mac users beware..
edit: was wrong its 10.5 not 10.5.1