I think the problem here is that Safari/OS X allowed the port to be opened. That shouldn't happen, but my question is, would it happen on a machine with the firewall turned on, because as I noted, the machines were all still in their default, out-of-the-box states on Thursday, and with Leopard, that means the firewall is OFF. And if it doesn't happen if the firewall is ON, under what conditions? If I put Safari in my list of programs allowing incoming connections, then does it allow ANY incoming connections on ANY port? From what I've read, the stateful-packet-inspection firewall, called ipfw, is set to allow all traffic through, so it's no help.
Also, from what I've read, the hack only involved clicking on the link - it didn't involve having to install anything (like a Trojan) so I don't think claiming that it's simply user stupidity, which therefore nullifies the seriousness of the security hole. Sure, lots of us run behind routers and this sort of thing wouldn't happen, but not everyone does, and with the way legitimate web sites are getting hacked these days, how can you be sure that the link you click on is safe if something like this is a possibility?
Anyway, I'm not concerned that this is a real-live-in-the-wild issue now - but Apple needs to fix it, and from all reports, are working on doing just that.