Writing on the Comcast Voices blog, Comcast manager of DNS engineering Chris Griffiths shares his experience at the recent ICANN key signing ceremonies, where he served as a backup crypto officer.  Griffiths also noted:

With all this momentum, several key top-level domains have also announced recently they are ready to support DNSSEC. The first was .ORG. The other major top-level-domain was .EDU. As these large Domain registries start to support DNSSEC, it allows domain holders like Comcast to sign our domains and make them secure.

Comcast maintains a DNSSEC information center with regular updates on its deployment progress, and it is a member of the DNSSEC Industry Coalition.  With more than 14 million high-speed Internet customers, it is one of the largest Internet service providers in the U.S.