In Leopard, many man pages (the documentation for Mac OS X's UNIX commands) are compressed with gzip. This is a very good idea but, if you upgraded to Leopard from Tiger, the old man pages are left in place by the installer (this is a bug).
So many man pages are there in two versions: the old uncompressed one from Tiger, and the new compressed one from Leopard. The problem is that when man searches for a given page, it finds the uncompressed one first and displays it, thus showing you outdated information. To solve the problem, the old man pages must be removed. I made a shell script that removes everything in /usr/share/man that is not installed by Leopard (I made the script by actually installing Leopard on a blank disk and comparing with my installed system). Here's the command to build the script:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071201021830891