The biggest problem with really speedy quarterbacks like Cunningham and Vick is that all that running means more injuries. The trick is finding one who can be trained to throw the ball away more often than he tries to tuck and run.
As far as Vince Young, the UT system just seems to produce emotional cripples for some reason. I've often noticed that Austin turns people soft.
He'll certainly be a great fantasy quarterback who will put up some impressive statistics over his career. Time will tell if he'll be able to consistently lead his team to victory, however.
Also, he seems to be practically indestructible like Tebow/Roethlisberger.