I wasn't very clear. It did originally go into /usr/local/man/man1/growlnotify.1 and when that didn't work, I cp'd it to /usr/local/man/growlnotify.1 to see if that would work.
To be clear: having growlnotify.1 in *either* location does NOT work...
UPDATE: I found one part of my problem. The manpath.conf file, by default, expects man pages in the /usr/shared/man/ directories, not in the /usr/local/man directories. A quick fix (as it were) was to cp the growlnotify.1 to /usr/shared/man/man1 and the MAN GROWLNOTIFY command works...