I think the ability to breakdown game film and understand a defense is right up there with arm strength and accuracy as far as drafting a quarterback is concerned. A QB could have the best arm in the world, but if he can't read a defense and stares down his receivers all the time, that arm will basically be rendered useless.
The Vikings may not get the chance to take a good QB in the first round, depending on where they draft. Stanford QB Luck is a top 5 selection. Jake Locker(who could be viewed as a hometown guy) has fallen down the draft boards due to his poor play. You just never know what QB you are going to get. If you take a QB in the first round, you could wind up with a Ryan Leaf, or a Peyton Manning. Or you might find a Tom Brady later on. In an offense like the Vikings, I would take a smart QB over one that has a cannon with no knowledge.