Most of all, I like the ubiquity. I can rely on it being on a system (particularly since I eschew Windows to the greatest extent possible), or can get it easily. Since I make some claim to be a Unix sysadmin, I feel it is essential that I be at least comfortable with vi. Anyone who makes that claim and who can't use vi is lying. You can't really call yourself a Unix sysadmin if you don't know vi, unless you prefer ed. I tend to use nedit or BBedit most of the time, but I'm not shy about using vi when indicated.