I've thought about this one on and off for several years.
 OK - my understanding is that use of the F-word is generally confined
to PG-13, R and NC-17 films.
 I simply don't remember any film other than "The Right Stuff" to use
the F-word a few times and still maintain a PG rating.
 Am I right that the Right Stuff is unique in this regard?

PCVentures..

Actually, there have been several films that have received PG rating
that contained the F-word.  "All the Presidents Men" released in 1976
and contained the use of the F-word several times.  Also released in
1976, Woody Allen's "The Front" used the F-word as well.  According to
Roger Ebert, these two films are the first PG rated films to use the
F-word.  Bear in mind that these films, as well as "The Right Stuff"
(1983) were released well before the PG-13 rating was instituted on
July 1st, 1984.  There obviously wasn't enough other content in these
films that warranted the jump from a PG rating to an R rating.  Since
PG-13 was put in place, according to the Motion Picture Association of
America (MPAA), the body that rates movies in the United States:

"A film's single use of one of the harsher sexually-derived words,
though only as an expletive, shall initially require the Rating Board
to issue that film at least a PG-13 rating. More than one such
expletive must lead the Rating Board to issue a film an R rating, as
must even one of these words used in a sexual context. These films can
be rated less severely, however, if by a special vote, the Rating
Board feels that a lesser rating would more responsibly reflect the
opinion of American parents"
MPA | Movie Ratings | About
http://www.mpaa.org/movieratings/about/content5.htm

So, in essence, you are correct.  Any films released after 1984 that
contain a single use of the f-word are immediately given a minimum of
PG-13.

I hope this answers your question.  If you need any additional
clarification, please let me know.

Regards,

-THV

Search Strategy:
F word PG

References:
Google Answers: Rated R for language
http://answers.google.com/answers/threadview?id=17456

MPA | Movie Ratings | History
http://www.mpaa.org/movieratings/about/content2.htm

Right Stuff, The
http://www.imdb.com/title/tt0086197/

Awesome answer!