Then, there's the problem of the input device. Ever enter a movie name for search using the TiVo remote, AFAIK the best currently available? It's a pain. Now, one thing Google TV gets absolutely right is that your phone will be your secondary interaction device for your TV.
The real interesting question here is: will applications on the Google TV set-top-box be able to access the tuner and EPG functions. TiVo has a nice SDK for their boxes for years now, the reason you never heard of it because they don't allow apps to access these features out of fear from content providers. If you can write Android apps running on the STB that can access the video stream, now that would be super, but I don't expect to see this anytime soon.