I've no idea why anyone would pay for this now that you can get Blue Coat Systems' excellent K9 Web Protection ( http://www1.k9webprotection.com ) absolutely free.

I am not affiliated with Blue Coat Systems other than being a very happy user of their product.

Mackey's comment about OpenDNS is true (I use it myself). It is a great resource, but a lot of adult sites still slip through the net. If you use that in combination with K9 then very little will slip through, and that which does can be reported easily and is acted upon promptly.