When I did follow the AVS forums awhile back, I was under the impression that the Guide Data was not provided by TiVo but by a third party, and that you could hack TiVo to ethernet and get different third party data that was more complete.
I think a big problem is that TiVo relies on someone else, that relies on the broadcaster giving out enough guide data info to utilize TiVo features to their full extent. I'm still hoping that TiVo sees the new season of "The Shield" and picks it up properly.

/me off to find out when "The Shield" season 3 premieres...
/edit March 9th!! WOOHOO!