The Day Without X
The Day Without X is a project with a simple premise. Unix and Linux systems typically depend on an X Window System server in order to display GUI applications. If one day you booted your workstation and X didn't start, and if you had work you absolutely needed to get done before you could begin troubleshooting why, would you be able to work? Or would you be at a complete standstill?
The nearest equivalent on Windows is Safe Mode with Command Prompt, but that environment is so incapable of any actual work (by design) that Windows users simply can't work at all if Windows doesn't boot to a GUI.
If you turned on your *nix workstation and it booted to a login prompt but didn't boot into X, would you still be able to work?