Take a recording from MythTV and then play it back in Windows. Does the quality still look poor? If not, then I'd say it's a gfx card driver issue on the Ubuntu side.
What gfx card are you using? I'm using an NVidia GeForce 8800GT with the official NVidia drivers from the Restricted repository and definitely have no visual quality concerns.
Take a recording from MythTV and then play it back in Windows. Does the quality still look poor? If not, then I'd say it's a gfx card driver issue on the Ubuntu side.
What gfx card are you using? I'm using an NVidia GeForce 8800GT with the official NVidia drivers from the Restricted repository and definitely have no visual quality concerns.