I've got an external USB-powered 320G iOmega drive on my wife's mini that's used for Time Machine that frequently disappears from the desktop, preventing TM from backing up. I'll unplug and replug the drive, and it appears again, and can be selected for TM, and all is well. The last drive I used for this suffered the same symptoms and eventually failed and could not be repaired. Is there something that can prevent an external USB-powered drive from surviving a restart, or mysteriously get interrupted somehow? Or cause it to not be automatically restored to the desktop after that happens? Is there a way around this? I have my own TM setup which uses my TimeCapsule, so could another mac somehow get confused and forget a local USB drive to try to use a nearby TimeCapsule instead? Anyone else have this problem or hear of it? Or have any suggestions? TIA!!