http://sports.ign.com/articles/604/604010p1.html
In a nutshell, QB vision passing will require your quarterback to look at the receiver he's passing to in order to have the very best chance of completing a pass. Other bonuses of looking at the intended receiver include having the option to lead him and place the pass precisely where you want it. That is you can throw behind or ahead of a receiver to keep the defense from getting to it and even that awesome stem route Chris Carter used to run with the Vikings where he wanted the ball just over a defender's head. But all of this only comes with looking at the receiver in the QB vision system.
The QB vision system will allow for some new strategies, however. In head to head as well as CPU games the defense will know who you're looking at so you can use this to your advantage by looking one way and throwing in another direction. On a play action fake, the quarterback will be late looking downfield since selling the handoff and the run is the whole point of the play fake. Also the cone of vision shrinks for every QB when he's scrambling since he'll be less focused on what's going on downfield.
In Madden you've been able to add some precision positioning on your passes for some time now, ever since Visual Concepts fine tuned Maximum Passing in the 2K football series. So the leading and placement you'll be doing in Madden NFL 2006 is more about the specialized animations that are going to go with it. You'll see receivers stretch for passes in front of them and pivot to position themselves between the incoming the pass and the defender. Fade routes will be a thing of beauty, just like in real life, now that your receiver will try to keep his feet in bounds to catch a ball thrown with perfect touch over his outside shoulder. Y