And once you have an account they can link it with your usage of their DNS and get a better price when they sell the data. As stated by its cofounder in the "n

And once you have an account they can link it with your usage of their DNS and get a better price when they sell the data. As stated by its cofounder in the "no more ads" post, OpenDNS is a "revenue oriented company" so it seems the logic behind this option existing for registered user sis that they get more money from selling registered user data than from showing ads.