As long as I am on the topic, I might as well explain this reach per million business. Alexa does not calculate the actual number of users visiting Web sites... what we do instead is release raw data about how many people in a sample population (Alexa Toolbar users, among others) visit a site. The data is normalized to a sample size of 1 million users so that the reach doesn't fluctuate as our sample base grows or shrinks.
Are you with me so far? So, for example, if we say a site has a Reach per million of 6000, it means that 6000 people in our sample of 1 million Internet users visited the site. Or, to put it more plainly, .6% of the population visited the site.
Where was I? Oh, yes Skype. Just for flavor, I added vonage on the graph. You can see that Vonage, despite millions spent on television advertising (I can't get that damn hill-billy vonage song out of my head "woo-hoo, woo-hoo-hoo") is virtually flat, while skype has more than doubled its user base.
Skype - skype.com - site info
