Yesterday I finally performed dreaded arch update on my local server. Everything went fine, but after reboot I couldn't ssh to it anymore. Not having external monitor and keyboard at that point (and for the past year) kinda bummed me out. And then I remembered I had some dinosaur PC parts in basement and among them keyboard. Monitor was easy - just use TV.
Here is a tip that could potentially save you several hours (Mountain Lion): if you have custom keyboard layout, put it in /Library/Keyboard Layouts and NOT in /System/Library/Keyboard Layouts. I know you shouldn't put stuff in System directories, but still... misleading.
BTW: Ukelele just made my life with Mac a little easier (while Mac itself took 2 hours from me by being inconsistent)