The Hotline writes: "Comcast is selling On Demand political advertising as an environment for candidates or advocacy groups to "elaborate on their causes." Since DVR advertising is not bound by the same constraints as television or radio, it allows campaigns to run spots of up to 60 minutes and gives viewers the freedom to decide which messages they are interested in watching. Comcast has even established a clearly recognized "Election 2006" link, uniformly positioned in all 22 available markets to make it accessible to the viewer when they want."
The article, which is much longer and more detailed than this quote, includes quotes from Joe Trippi as a bonus.
Earlier:
Comcast Expands Ads-on-Demand Service
Comcast, TiVo to Insert Updated Ads in Old Shows