Update to original post: Utilising Facebook Chat (without needing to be on Facebook) Facebook Chat can now be used with chat clients that support Jabber - this includes iChat, Adium, Pidgin and AIM.
Facebook has kindly provided a page to help users setup here: http://www.facebook.com/sitetour/chat.php
I've managed to successfully set it up on both Adium and iChat. With Adium it seems to work better with Jabber rather than the current Facebook chat feature included in Adium (which isn't really supported by Facebook).
It's good to see that Facebook is finally providing a Jabber service, as it now makes it a lot easier for members to utilize their chat system without needing to constantly be on the site.