A week or so after installing Tiger on my Panther-original G5 I noticed some slight slowing of my system, so I ran the Tiger disk to repair disk, ran repair permissions from the system itself, and then decided to run the original AppleCare TechTool Deluxe disk. I had checked the Apple site to see that there wasn't any warning not to do so. That was my big mistake. Techtool Deluxe deleted a number of vital system files from the Volume Structure and my system was shot to ****. It wouldn't start up and of the few ways the drive could be recognized, only one was available (that gave me some hope, but)after lengthy discussions with Apple and the Apple Store personnel, I was instructed I had no choice but to erase and install. Fortunately, one Apple tech person recommended I try Firewire Target Disc mode with firewire cable (6 pin to 6 pin cable) and connect with another OSX Mac (in my case a Jaguar eMac). Despite my G5 system not being able to start up, target mode did provide drive access to the eMac and I was able to copy the files I needed before the reinstall. What a relief. Annoying to have to reinstall everything, but alot better than nothing. Any suggestions on some kind of reimbursement from Apple, i.e. the price of a utility disk, maybe $100? The Apple tech person also stated that the current AppleCare discs which are sent out with new machines include the same software as the one which came with my Panther G5, so even if you think yours may be a helpful utility, don't run TechTool Deluxe from your AppleCare disc.