The beta version was just released for those who signed up for it on 360. It will supposedly be coming to similar devices as Netflix (not just consoles, but blueray players, etc) in the next 18-24 months.
It's pretty slick. Higher quality (Could be HD?) and much smoother. Live games, Game replays, Several different ESPN shows including sportscenter on demand, Mike & Mike, Around the Horn, Rome is burning, etc.
Far superior than watching this stuff on my PC.