One reason why google talk is interesting (and you should like this burg) is google are supporting open standards..
So they are using a SIP phone solution for talk and basing thier IM on jabber.. If you know about Gizmo which is an IM and phone VoIP application then you will be aware that this solution is already linking US college campuses, hardlinbe numbers, SIP hardware phones etc.. With googles massive input into the field this may go a long way to unifying the IM and VoIP space..
I have long been a skype fan.. That in turn has had me playing with SIP phones and technologies to test but quite frakly once I got my parents, non techie mates, brother, etc all to use Skype (they all love it BTW) getting them to install and more importantly configure the ports for SIP phoneing was a bridge to far.. With luck Google talk (using gizmo for me) will solve these issues and get them on an open standards system..
Click here to read 'Micheals minute' on the issue.. He is the guy behind Linspire and many many other open source projects (including gizmo)..
http://www.michaelrobertson.com/