Sadly, I still haven't had time to properly respond to Ed Heckman's difficulties with the Church's beliefs concerning Mary. I did get one answer to my call for rebuttals from the peanut gallery. Here's Anonymous' defense of Marian doctrines. The opinions expressed by him/her may or may not reflect my beliefs or the beliefs of the Church.
1. Ed's first point is that Mary cannot be the most perfect example of human faithfulness because: a) she's no more faithful than Abraham; and b) she seems to have had doubts over the course of Christ's life.
In response, I would note that: a) Before God asked Abraham to be faithful, He promised Abraham a number of rewards for faithfulness. See Gen. 17. But He promised nothing to Mary directly, yet she was nevertheless willing to do his will. See Luke 1. Being faithful without knowing what the consequences will be is better than being faithful for a reward.
And b) the doubts that Mary had were not, as Ed claims, evidence of a weak faith; they were tests of faith that Mary passed. Simeon warned Mary that "you yourself a sword will pierce," Luke 2:35, and his prophecy came true in each of the instances Ed cites. See this.
2. Ed's second point is that Mary cannot rightly be considered a sinless "New Eve" because: a) she calls God her Savior in Luke 1, and the sinless do not need a savior; and b) there is no explicit scriptural support for Mary as a sinless "New Eve."
In response, I would note that: a) you can "save" people in two ways: getting them out of trouble, or keeping them from getting into it in the first place. Knocking someone out of the path of a speeding car saves that person just as much as providing medical care in the event that he is hit. God saved Mary from sin by keeping her from it; he saves us from sin by getting us out of it.
And b) Ed is right that there is no explicit scriptural support for calling Mary a sinless "New Eve." But this is not a problem for Catholics, who don't demand explicit scriptural support in the way that Protestants do. Catholics believe that the Church came before the Bible in that it preached before the Bible was written, and it chose the Books that were to become part of the Bible (choosing the synoptic Gospels over the gnostic ones, etc.). For this reason, the Church can proclaim a doctrine without explicit scripural support, for the Bible is a creature of the Church, and not the other way round.
It seems Jay is having similar discussions at Deo Omnis Gloria.
Linguistic Issues Regarding the Perpetual Virginity of Mary [regarding Jesus' "brothers"]
Linguistic Issues Regarding the Perpetual Virginity of Mary, Part II [regarding Joseph not knowing Mary "until" Jesus' birth]