Our sales people are regularly asked by clients, especially ad agencies, for demographics on our site visitors. These buyers of advertising want to be sure that they'll be running their ads on a site that will help them reach their desired target market, whether that is college students, recent graduates, U.S. residents, or some other group.

But how do you get a rough idea of site demographics if they can't provide them to you, won't provide them to you, or you don't want to ask for them? Try sites such as Quantcast. Their methodology is somewhat flawed as they typically don't have access to the web site's server logs so at best all they can do is estimate the number and make-up of users to whatever site you're researching. Sites such as Quantcast typically do that by adding their tracking software to the computers of thousands of users. These users typically do so in return for being paid or provided some other type of incentive. That system ensures that they're not random and therefore not representative of the overall Internet population so you need to take the results with a grain of salt, but some information is usually better than no information.