Steve Garfield, a blogger in the Boston area is one of the lucky few to get the first deployments of TiVo's software on the Comcast/Motorola boxes (reviewed here in 2005). The comcast/tivo deals were announced a couple years ago and pushed back time and time again, but it's finally becoming real.
Steve's story of signing up and receiving the software mentions that he was actually the very first customer to get it. His story mirrors a lot of my experiences with first deployments like this (I'm getting FiOS internet/TV today after waiting for two years), with customer service people confused and claiming the service isn't available.
He's also posted a bit about how fast forwarding is different and has an entire gallery of screenshots over on flickr. For comcast customers waiting the past couple years for this deal, keep an eye on his blog to hear how it works out. It just may be that the Motorola box running TiVo is a better deal than buying your own TiVoHD and paying the monthly price.