I've tested it n800 user to n800 user with non google talk account (regular jabber account, standard xmpp) and it works great! Face to face video conferencing, I was impressed.

Now it seems all that was needed was a compatible client. I have no idea if this is standard XMPP video conferencing or if this is something special outside of the Jabber protocol but it worked just fine n800 to n800 user. The video looked as good as one might expect.