PVRblog pointed out that Steve Garfield is blogging about the Comcast deployment of TiVo software on their existing Motorola DVR set-top boxes. I found an article on Steve's site that includes a Ustream video tour of the Comcast / TiVo user interface. Overall, the experience looks similar to the TiVo Series I and Series II experiences that I've had in the past, although Steve is complaining in the video about speed and navigation issues.
I'm sure that there are more good articles on Steve's blog (offonatangent.blogspot.com) that talk about other aspects of the Comcast / TiVo experience. I haven't had time to read them yet.