I was getting anoyed being unable to share my Address Book, so I put together a little freeware application which allows me to transfer my entire Address Book, groups, or individuals to my local LDAP directory. Other clients on my network simply connect to it. Download AddressBook 2 LDAP from my site.
[robg adds: I haven't tested this one...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040220220647975