magic numbers

[Spencer W. Thomas]

The ONE thing that putting #! into the kernel gets you that having 
exec(2) do it (besides putting it in probably a more obvious place),
is to allow setuid shell scripts.  This gives shell scripts an equal
footing with all other programs - you don't have to explain to users
that if they write a C program and chmod u+s it works, but if they
write a shell script and chmod u+s it doesn't.

=Spencer