Robert X. Cringely looks at the utilization model behind Skype and estimates that no more than 900,000 people can be talking at one time. It’s not the six million or so connected users, but that’s pretty good, especially for free. Of course, Cringely points out it’s not really free if you’re one of the supernodes. My computer was. Then I changed a few firewall rules and watched our network traffic drop.