Personally, I want voice recognition on my TV because wherever I am my controller is not.
For example, if I am at the computer and the controller is on the lounge, I want to say "TV: Change Input HDMI3" so it switches the TV to ATV2 and I can play video or music from iTunes to the TV.
Or, since I have an Airport Express as well so that I can watch the cricket and the wife listens to music instead of the commentary, to turn it back to TV sound on my HIFI when something exciting happens and I want to hear, I want to say "HIFI: Change Input Digital In" and after that "HIFI: Change Input Auxiliary" to return to the AE.
Voice recognition for common basic commands would be useful on all the devices. eg Volume Up, Volume Down, Channel Up, Channel 10, Menu, TV Guide, Fast Forward, Pause, TV Off, Mute, etc.
Maybe Logitech can add voice recognition to their Harmony range.