Me and Peter Krantz just tried to get an iChat video chat going, just to test it out. We never got it going.
We forwarded a gazillion ports on our routers, turned off the firewalls on our laptops but to no avail.
The thing is, had we managed to get it working it would still have been way too hard to set up for any sort of reqular use. And how often do you have access to the router anyway?
This tells me that iChat is primarily made for internal, LAN based use. Am I wrong? Too bad if I am not.