Earlier this summer when someone told me that you could hook two Macs together with a firewire cable, boot one up while holding down the "T" button and access its drive from the other like any other external firewire drive, I never actually thought I'd use it.
Today, while working on one of my daughters' Macbooks, I screwed up the hostconfig file while trying to edit it with TextEdit (I know, I should have used VI to start with). I should have guessed that TextEdit wouldn't leave the file without a file extension, but I didn't. So, when I rebooted (or tried to), the machine hung with some funky error in white text on a black screen.
So, I hooked it to my Macbook Pro with a firewire cable, booted it into disk mode and voila, there was the volume listed in my Finder view. A few simple commands in the terminal window (ie renaming hostconfig.txt back to hostconfig), eject the volume and reboot her Macbook and we were back in business.
I did learn from my mistake however and use VI to edit that file on the other daughter's Macbook. All my moaning and groaning about how archaic VI was over this past summer has turned into a pretty big chunk of crow.
As long as you're learning, you know you're still alive I guess.