> Because even allegedly compatible shells differ subtly, you run
> the risk of having a key startup script fail - and maybe not right
> away, but after installing an update.

Any specific examples of how changing root's shell can break startup
scripts?

I am not sure if I understand this. By startup scripts, I think of two
things:

- the /etc/rc (and related scripts), but these have the program to run in
  the first line (#!);

- and root's actual login scripts, i.e., /root/.login, /root/.profile.
  but usually these scripts are only read and used by the appropriate
  shell (for example, csh is not going to use .profile and ksh is not
  going to use .login). I could see a problem if these scripts were
  changed or read and used (sourced) instead of executing other
  incompatible scripts.

   Jeremy C. Reed
   http://www.reedmedia.net/