In chronological order, with highlights pasted here:
From TurretinFan -
Response to Jay Dyer on Calvinism (Part 2 of 13)
The Nestorian error is (to put it concisely) to deny the hypostatic union. Nestorianism, as it is classically defined, argues that Christ was not one person with two natures, but two persons. The existence of the hypostatic union is critical to the Calvinistic view of the atonement...The fact that the person of Christ had a truly human nature made the atoning death of Christ possible, as well as making the form of the sacrifice (death of man) a proper suffering of the penalty due. Without one or the other, the atonement would be impossible. Consequently, it would be impossible for a consistent Calvinist to embrace Nestorianism.
In the years since "theotokos" became accepted terminology, Mary grew to have an increasing role in the worship of Rome, until today we have apologists for Catholicism insisting that devotion to Mary is a mandatory part of religious life. Now, an official document from the Vatican from the 1970's states: "With his mind raised to heaven ... the priest should very often turn to Mary, the Mother of God, ... and daily ask her for the grace of conforming himself to her Son." (source) If Nestorius were still around today, he'd feel vindicated in opposing the term "theotokos" on the ground that it can lead to what amounts to Mary-worship... (last link added)
Further Response to Dyer
...it does not appear, on the historical record that we have before us, that Cyril accurately represented Nestorius in his characterization's of Nestorius' views. I'm not sure why Dyer is so set on defending Cyril on this point. Why not just admit that Cyril was fallible, and may have misunderstood Nestorius for a variety of reasons?
From Vox Veritatis -
If Mary is the Mother of God...
...saying that Mary is the mother of Christ, rather than the mother of God, does not make one Nestorian, but rather saves one from an absurd logical conclusion.(Thus reflecting my words here: She bore the HUMAN Jesus, Who was God and man. Jesus was her Creator. She bore His humanity... It is more correct to say The Person who came from her is man. And it is MOST correct to say The Person who came from her is the God-man.)
1. Mary is the mother of God.
2. God is the Trinity.
3. Therefore, Mary is the mother of the Trinity.
This is absurd, but it gets worse.
4. Both the Father and the Holy Spirit subsist within the Trinity.
5. Therefore, Mary is the mother of both the Father and the Holy Spirit.
This is patently absurd. On the other hand, it is accurate (and logical) to say that Mary was the mother of the incarnate second person of the Trinity. That is, to say that Mary is the mother of Christ. Such an assertion maintains the unity of Christ's natures in one person, without the logical absurdities of saying that Mary was the mother of God. Thus, it is logically coherent, and not Nestorian (in the Christological sense)...
...Jesus and God are not logically identical. God is a trinity of Father, Son, and Holy Spirit, and thus to identify Jesus as God, in the second sense, is to assert a modalistic view of the Trinity (since Jesus, encompassing the meaning of "God," must also encompass the Father and Holy Spirit, in which case the most logical explanation is that there is only one person who manifests himself in three different ways). Unless one wants to assert modalism, one cannot say that "Jesus is God, Mary is the mother of Jesus, therefore Mary is the mother of God."
And again from TurretinFan -
David's Relationship to God
The only argument for the expression is that Jesus is God, Jesus is the Son of Mary, therefore Mary is the mother of God. But Jesus is also the Son of David. Any takers for calling David "the Father of God" or the "Ancestor of God"?
Finally, this fine post from Vox Veritatis deserves to be read in its entirety.