I find myself a bit frustrated with the state of Orthodox apologetics surrounding the question of the Immaculate Conception of Mary. While I am quite sure that there are competent treatments of the question around, I haven't yet found a discussion that didn't make elementary mistakes about the Catholic understanding of original sin (a mistake I've seen even in such an otherwise excellent book as For the Life of the World by Schmemann). I'm not a trained theologian, but I do feel competent to make the following observations.
1. While the Immaculate Conception hasn't been adopted widely in Orthodoxy, it does have a place in Orthodox tradition. St. Seraphim of Sarov, for instance, believed in the Immaculate Conception. So Orthodox apologists shouldn't be so quick to label it a "western heresy."
2. The Catholic Church, both Latin and Eastern Rite, does not teach that original sin involves inheriting actual guilt. Rather, the Church teaches that it involves inheriting a human nature which (among other things) is now prone to sin in a way that it wasn't before the Fall. St. Augustine does appear to have been of the opinion that guilt is inherited, but the Church has rejected this position. See for example CCC 405.
Although it is proper to each individual,295 original sin does not have the character of a personal fault in any of Adam's descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.
3. The exemption of Mary from inheriting original sin does not make Mary superhuman. It merely makes her not subject to concupiscence (the tendency to sin), without necessarily preventing her from being able to sin. (Though obviously the Church teaches that she didn't actually sin either.)
4. The occasional Orthodox apologist who argues that the Orthodox churches don't believe in the Immaculate Conception because they don't believe in original sin, should consult some Orthodox Catechisms. Yes, the understanding of what original sin entails is different, but that is not the same as not believing in it at all.
There is a huge amount of agreement between the Catholic and Orthodox churches regarding mariology, so it annoys me to see mistakes like this being made so often. Also, I would like to do some more reading on Orthodox mariology. Anyone have suggestions?