Nasty upgrade bug: if you upgraded OS X 10.4 to 10.5, the installer left your old manpages in place. It also added the new ones, gzip compressed, but man finds the old ones first.
The summarized fix:
find /usr/share/man -exec test -e {}.gz \; -exec tar rzvPf ~/man.tgz {} \;
sudo find /usr/share/man -exec test -e {}.gz \; -exec rm {} \;
Your 10.4 manpages will be backed up to ~/man.tgz and then removed.
If you have a case-sensitive file system, see the comment by sEEKz on the hint page.
16 December 2007