I have no idea why Comcast is dragging their feet so much on the Tivo software rollout. Are there compatibility issues with the software and their installed base of boxes? Who knows? All we do know is that it's at least another year of swearing at the absolutely awful DVR interface they ship now:

Comcast first announced it would be using TiVo's software back in March 2005 and expected the majority of Comcast markets to be fitted with TiVo by mid-to-late 2006. However, only this month has Comcast began testing TiVo software on Motorola boxes with a handful of Comcast employees.

Comcast won't actually begin its first actual market trial until spring of next year and refused to comment on whether the TiVo service would be available to most Comcast subscribers by the end of next year.

The Comcast DVR is so bad that's I'd rather watch standard definition TV with the trusty ReplayTV. Yes, it sucks that bad...