People who have tested the demo version of Project Natal have complained of a very slight lag between a player’s actions and the onscreen response. Now MTV has run some tests to time the delay and pinned it between .08 seconds to .12 seconds, with an average of .10 seconds.
This delay means that it will be difficult to play games on Natal that require very quick responses from the players, such as jet simulators and high speed racing.
However, every other feature of Natal, including vocal commands, facial recognition, and heck, even just spotting your exact position in a room, have performed perfectly.