I have a user in my department who has been complaining of problems using his Mac Pro with a Western Digital MyBook via USB or Firewire, for the time machine automatic backup system. He says it works fine if he plugs in the hard drive and runs a manual backup. But then, he'll return a few hours later, and then the hard drive will no longer be visible on his desktop and all subsequent automatic backups will have failed. I assume this has to do with the external hard drive powering itself down. Seems stupid that there's no 'keep-alive' signal being sent to it to prevent that. Is there any way to fix this problem for him? Or, barring that, is there a particular model of hard drive that MacRumors members are recommending for Time Machine usage - one that won't disconnect whenever it feels like it? Thanks!