I've been using the 5.8 ghz transmitter for about 2 years. First with my DirecTivo and now with my HR21. It feeds a SD TV in my bedroom about 30 ft. away from my main AV rack in the living room through 2 walls.
It works ok but just ok, not great or spectacular, just ok. About once a week I have to readjust the antennas a little. For some reason the signal will just go flaky and a little tweak to the bedroom antenna brings everything back.
I would not use this setup with a HD TV, don't think the results would be favorable. Later in the year when I upgrade my bedroom TV to HD, I am either going to install an HD receiver or use video baluns over CAT5.