Hehe no need to add a disclaimer here

With free accounts you are paying for the advertising, you are paying for the site which you are giving out for free.

A lot of companies run on a business model of offering a lot of free accounts along with premium accounts which can be used to cover a lot of thier costs incurred by giving out the free accounts.
Netfirms have a similar model to this but they dont just go on upgrades from free to premium or people purchasing premium accounts, they also advertise on all free sites they host.