IMHO, "It" is basically a belief by teammates, fans, coaches, etc, that no matter what happens during a game, their guy can pick himself up and lead the team to victory.
Does Leinart have "it" this early? Based off of his college career and what he has done it two games, maybe he is on the road. Does he have "it" at the same level of Brady or Montana? Hell no.
Can guys lose "it" or find "it" later in their career? Absolutley. I think Farve had "it" for a decade but is quickly losing "it". Does a guy like Brees now have "it"? Hell yeah.