Microsoft hopes to have 5 million units available for purchase worldwide at the time of launch, some being sold with a 360, and some being sold on their own. The price would range anywhere from £30 to £50 (what the price would be in USD is anybody's guess at this point) and would have a fairly robust 14 launch games.
We know that Criterion/EA had modified the popular Burnout Paradise to work with Natal, so maybe the 14 includes patches for some games. I can also assume that of the 14 games, a large chunk of them will be arcade/mini-style games, as opposed to large scale games like Call of Duty or Assassin's Creed. At E3, Microsoft showed a painting game (actually, it's more of a program than game...), a brick destroying game that you've all seen on Youtube by now, a driving game (Burnout), and Lionhead Studio's Milo, which suffice to say kicked ass. I doubt that Milo would be available for anything outside of closed doors, but the other three games seem likely to see daylight.
Sony's PSEye motion controller is scheduled to come out next Spring (at least in Japan) and is likely to at least have Resident Evil 5 as a launch game. While it's all wild speculation about Natal, we can only hope that it's more evidence that Natal is coming 2010 as opposed to 2011.