My first thought watching Skype be demonstrated on a 55-inch (140cm) Panasonic Viera Cast TV was that it's going to be incredibly useful - though a bit laggy - way to keep in touch with family and friends. My second: Ac-TING!
Skype 4.2 on TV really is a natural fit, even if the Panasonic Repertory Company using it are a little stiff. The 720p picture is clear (though not crystal), and the lag wasn't at all unbearable. It's impossible to say how good the sound was, since the actors were mic'd up and... uh... a metre away from one another.
You can also communicate between any combination of TV, PC or mobile device that's Skype-equipped. As for how Skype will physically affect your home theatre, the webcam Panansonic was barely noticeable on top of the Viera.
The Viera Cast TVs will launch in Q2 2010, but it's clear that Skype 4.2 is ready for action right now.