Waaaaay back in Arcview 3.x you could open an .apr file in notepad (or VI - mwahaha) and fix it if something happened. Now - you've got squat if your mxd goes south. Heck you can even edit a Quantum GIS project file if something goes wrong....not that I have or would use Quantum GIS - I know a guy who knows a guy who said you could...... . So make the mxd a xml/text based file you can fix. I want to open my MXD in vim.