• Lack of content (Apple and Amazon are in the process of fixing this, but Ubuntu won't have the weight to get Big Content on board)
• Linux hardware is a pain to hook up to HDTVs
• Unity interface is poorly suited for 10-ft interaction
• Existing players (Apple TV, XBox 360, Boxee, etc. -- even Google TV!) are more mature and have had time to strike content deals
In short, too little, too late. IMHO, they should concentrate in stopping the user bleed from their desktop distro.