I have two user accounts on my system, one for home and one for work. However, I have my contacts for both users in one big database because I sync to one Palm Pilot. As far as I can tell there's no cheap, easy, processor-efficient way to share an Address Book database between two users on the same computer (Apple, are you listening?). So I created this Terminal script to copy the Address Book files from one user account to the other, and then run Address Book.
Whenever I want to use the Address Book I double click on this rather than on the Address Book itself. This means that when I make changes in Address Book as one user, the changes will show up for the other users, so long as I run this script. You will of course need a slightly modified version of the script for each user account. It's quick, it's dirty, but it works.
sudo cp -R /Users/user1/Library/Application Support/AddressBook/*
/Users/user2/Library/Application Support/AddressBook
This will copy the files from the last user to modify the address book to the current user.
sudo chown -R user2: /Users/user2/Library/Application Support/AddressBook/*
This will change the owner of these files to the current user so that the files can be modified.
open /Applications/Address Book.app
exit
This opens Address Book and exits the script.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040613145925208