I have an older HDTV that can output 480ip/720p/1080i via Component and DVI(HDCP capable). I can confirm this wavy/scanline issue with the TV on my HDTV which does not happen if I hookup my MacMini, PS3 and set it to 720p.
I hooked up my TV to my computer monitor that has HDMI input and it works fine.
I'm guessing it might have to do with signal, clock timings. Could be fixed it in next update.
I'm not so uber excited with TV, partly because my HDTV was bought in 2003 just before HDMI became a standard. On top of that there's the optical to analog audio conversion I had to buy.