I finally got around to adding the XMPP profile field to the forums. This means that if you use XMPP/Jabber (including GoogleTalk etc) you can now put your address in there. It wouldn't display online status (yet) but will allow you to simply click someone to add them to your XMPP client
I've now added my XMPP address to my profile so if you wanna see what it looks like, just look over <----- there (it's the little trendy light bulb).
To set your address, just modify your profile, it's right there with MSN, Yahoo!, ICQ and AIM.