The detail that stands out the most in the listing is that camera will only support two active players at a time while tracking up to six players. This is probably best explained by the limited 57 degree horizontal field of vision. Anymore than two individuals playing at a time likely won't fit into what the camera see no matter how large their living room might be. So while Kinect won't support four players at a time it does support more than two players at a time, it will be able to handle players dropping in and out during party type games.
Other notable details include the cameras two resolutions (320 x 240 and 640 x 480) at 30 frames per second. 30 frames per second is what most games run at so its unclear at the moment what affect this will have or whether or not the camera will be able to pick up the subtle and fine movements like finger movement.
The complete spec is below.
Colour and depth-sensing lenses
Voice microphone array
Tilt motor for sensor adjustment
Fully compatible with existing Xbox 360 consoles
Field of View
Horizontal field of view: 57 degrees
Vertical field of view: 43 degrees
Physical tilt range: ± 27 degrees
Depth sensor range: 1.2m – 3.5m
320×240 16-bit depth @ 30 frames/sec
640×480 32-bit colour@ 30 frames/sec
16-bit audio @ 16 kHz
Skeletal Tracking System
Tracks up to 6 people, including 2 active players
Tracks 20 joints per active player
Ability to map active players to Live Avatars
Live party chat and in-game voice chat (requires Xbox Live Gold Membership)
Echo cancellation system enhances voice input
Speech recognition in multiple