I don't have a Tivo, I've got UTV. But I plan on getting a HD Tivo, when they come out later this year, I don't know exactly when.
Ultimate TV is basically done, no one at Microsoft is working on a next generation.
Some people here have stated they prefer UTV over Tivo after switching, but I don't think you give up MAJOR features, just little things. HD image will definitely overcome that for me.
Matt