I would not like to see ISPs block alternative DNS services. I use OpenDNS to block distracting sites, and alias http://block.opendns.com to localhost, which is then redirected to my to-do list. A web server on my machine redirects the default page at localhost to my to-do list on http://rememberthemilk.com.

In addition, my /etc/hosts file includes the hosts file from http://www.mvps.org/winhelp2002/, which aliases ad and tracker site domains to localhost.

Ad blockers suppress ads, but do not provide positive reinforcement. Site blocking software systems filter unwanted content, but do not substitute desired content in its place. It's not enough to slap the user's hand.

The domain name filtering service OpenDNS displays a block page at http://block.opendns.com if a site meets the criteria for filtering. This is negative reinforcement. OpenDNS might provide positive reinforcement if users could to substitute something else, for example, an online to-do list such as http://rememberthemilk.com, for the block page.

Maybe OpenDNS could provide such a service.