The problem with this approach is that they are offering an extra 0.5 miles per dollar only on the amount you spend, but Ferdinand Magellan wants to earn on money he is not spending. Also, there are other cards which award 1.25, 1.5 or 2 miles per dollar for general spending with no bank account requirement.
I really hate to drag us off my own topic, but I have to ask: which credit card offers 2 miles per dollar for general spending?