I have Cablevision and they technically allow you to opt out. But even after opting out, I still get that damned useless ad-infested search page sometimes, seemingly at random. I'm not sure if it's because of their incompetence of malicious intent.

Comcast has disabled all DNS hijacking, and has since they implemented their DNSSEC validating servers.

Yeah, I think you are right. The "Domain Helper" options no longer appear in my accounts page:

http://dns-opt-out.comcast.net/help-index.php

If you're using Comcast Business, I've yet to find a way to do this. Comcast Support (email, phone, live chat) also have no idea. If anyone knows how to do it, please let me know.

That's crazy. You'd think the business version would have more customization available, not less.

I take it you've logged into your comcast.net account and the box to disable it isn't there for you?