You just better hope you never have to scratch your head.... or sneeze.  You'll throw a grenade into your teammate or send your plane into a nosedive. 

But I'd say it will probably work well for games like Dance Dance Revolution and things of that nature.

I bet the hard core games wont use Natal.

When I read the OP, my thought immediately turned to the space/setting issues rather than the technical ones.

We have seen/heard that Natal will recognize multiple people/sources of input. What we may not know is its field of vision size. In other words, how spread out can they be.

But regardless, how big of a room will you need to get four people playing? That is the main question. Two will probably work most places. But beyond that, most rooms probably will not work very well. We all don't live on a sound stage like where the demos are held.

Mike from Morgantown

Four players would be hitting and tripping over each other.

Natal is only for the 360, so no. And besides, games won't all be for Natal. We'll still see a whole lot of classic games.

Cant charge you additional (and unacceptable) fees for local multiplayer.

Microsoft will zap it asap.

I imagine it would work the same as 4 player co-op on Wii. I've had 4 people all in a 12 x 19 foot space playing the Wii without hitting each other. Natal can track 20x20 or something if I remember right.

You mean those bastards won't charge me for 4 controllers at $50 a piece? How dare they do that to me?!?