See
this thread for my comments on the rpc message during the shutdown.
However, Sun supplies two versions of the shutdown command: /usr/sbin/shutdown and /usr/ucb/shutdown. The latter will understand "shutdown now" while the former will not.
The ucb version of shutdown is undocumented on Sun so I never use it on a Sun. But referring to my 4.3BSD manual, "shutdown now" will only take the system to single user mode. "shutdown -h now" will halt the box. And "shutdown -r now" will reboot. And all of this jibes with the HP-UX version of shutdown which is decended from the BSD version.
"When in Rome, do as the Romans..." I think you would be better off switching to /usr/sbin/shutdown on Sun boxes. First of all it is documented. (which won't help you until you install those man pages) And secondly, it is what most Sun people expect as you can see from Hassan2's comments. If you are going to continue using /usr/ucb/shutdown, at least mention this explicitly. A lot of Sun users don't even know about /usr/ucb/shutdown.