I hate the fact that you can open .doc files with many editors. When sending them around, there's always someone who opens and edits an OpenOffice file in Word

I hate the fact that you can open .doc files with many editors. When sending them around, there's always someone who opens and edits an OpenOffice file in Word or vice-versa which ends up messing up the file in some subtle and unfixable way. Having a single (extensible) editor is definitely the way to go.