Concurrence leads to occasionalism. You can't paint a nude without painting her a specific way; you can't carve a wooden flute without carving it a certain way; so also, God couldn't will that something exist without willing that it exist a certain way, with determinate features. But then everything's being the way it is at any point in time is explained entirely in terms of God's willing it to be so at that time, in which case (1) there is no need of secondary causes, (2) God actively wills evil events to occur and so is directly responsible for them, (3) there is no libertarian freedom of the will. I've written a few posts on my blog on occasionalism, if you want to see more in-depth arguments for (3).This, I think, is naive and is not a very careful consideration of the difference between concurrentism and occasionalism.
The doctrine of divine concurrence holds that for any even that happens, at the exact moment of that event, both the creature and God are causing the event at the same time. So when it comes to acts of free creatures, the creature has a distinct will that chooses something, but God is at the same time enabling, providing the power for, and carrying out the event.
Occasionalism holds that for every event that happens, divine causation is all there is. It is maximal, and there exists no causation by a separate agent.
So, when Steven says that, "You can't paint a nude without painting her a specific way; you can't carve a wooden flute without carving it a certain way," he is not recognizing that on the concurrentism view, it requires that a separate agent need to exist to decide to and also take part in the painting or flute carving such that God would only be causing the events that the other agent had chosen to carry out. As Arminius stated, "The concurrence of God is not his in, mediate influx into a second or inferior cause, but it is an action of God immediately flowing into the effect of the creature, so that the same effect in one and the same entire action may be produced simultaneously by God and the creature."1
Arminius further explains that when God has decided to permit a rational creature to act, He obviously would not refrain from giving the power to carry out that act. "Though this concurrence is placed in the mere pleasure or will of God, and in his free dispensation, yet he never denies it to a rational and free creature, when he has permitted an act to his power and will. For these two phrases are contradictory, 'to grant permission to the power and the will of a creature to commit an act," and "to deny the divine concurrence without which the act cannot be done.'"2
Arminius explains how this separates God from the sin He concurs in carrying out:
But this concurrence is to the act as such, not as it is a sin: And therefore God is at once the effector and the permittor of the same act, and the permittor before he is the effector. For if it had not been the will of the creature to perform such an act, the influx of God would not have been upon that act by concurrence. And because the creature cannot perform that act without sin, God ought not, on that account, to deny the divine concurrence to the creature who is inclined to its performance. For it is right and proper that the obedience of the creature should be tried, and that he should abstain from an unlawful act and from the desire of obeying his own inclinations, not through a deficiency of the requisite divine concurrence; because, in this respect, he abstains from an act as it is a natural good, but it is the will of God that he should refrain from it as it is a moral evil.3
In other words, God first permits the sin, and is then the effector of it. If the rational creature had not have chosen to sin, God would not have concurred with it and it would not have happened.
I think it's obvious that God working with a free creature in causation is leaps and bounds separate from God being the only cause, and that concurrentism does not entail occasionalism.
I personally am not even sure if holding to divine concurrence is necessary. I think the third option other than occasionalism and concurrentism, conservationism, is also a viable position. I think God has so ordered the universe so as to be completely in control and yet does not need to cause all events, yet He must conserve all things in being for them to actually exist. He must allow all events, and in the case that His ordering of events actualizes them He in a far removed sense is a reason for them coming about. However, that view doesn't seem to be one that has been traditionally held to by classical theists. Maybe someone could explain the reasoning to me?
1 James Arminius, WORKS OF ARMINIUS - THE RIGHTEOUSNESS OF GOD'S PROVIDENCE CONCERNING EVIL, http://www.godrules.net/library/arminius/arminius28.htm