Now that Google has its own instant messenging service that works with Jabber and iChat (talk.google.com), it'd be great to quickly add all your Address Book contacts who have gmail accounts (the only requirement for using Google's IM service) to your Jabber contacts list in iChat.
Well, remember this hint I submitted a while back to give Jabber accounts to all your Yahoo contacts? I just modified it to add a Jabber account of the form Johndoe@talk.google.com for everyone who has an email of the form Johndoe@gmail.com in the Address Book. Then you can just search for all your contacts that have gmail in them, and drag them into the Jabber contact list (once you've set up the gateway with talk.google.com, as explained on the Google Talk site).
Just paste this script into Applescript and run it. There's a fast way and a slow way to do so, as explained in the comments of the script itself.
[robg adds: I haven't tested this one...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050824194947849