At one presbytery meeting I attended, a (seemingly fairly conservative) ordination Candidate was being questioned about his personal statement of faith. Someone asked why he didn't include "the virgin birth" (by which most people mean what is technically called "the virgin conception"). He had simply forgotten to include it.
But I have asked myself whether, when I read my personal statement of faith before presbytery, I will include the virgin conception of Christ. If I do not, and if I am asked why, I will explain that whether or not Jesus was born of a virgin is not essential to the Christian faith, and does not change the message of the gospel. Jesus could have been fully human and fully divine even if he had been born in the natural way. If God had wanted to do it that way, he could have. And it would have been no less a miracle.
But affirming the virgin conception of Christ is important for a couple reasons--not as a litmus test for orthodoxy, but as an indication of some underlying attitudes. It may indicate whether one believes that miracles are possible. It is a mistake to reject the virgin conception because of an underlying belief that miracles simply do not happen. In that case, one would also have to reject belief in Christ's resurrection, which is essential to Christian faith.
Also, one's belief in or rejection of the virgin conception is an indication of whether one accepts the canonical Gospels as being generally historically reliable. If one believes that the writers of the Gospels were just making stuff up with no basis in reality, one is no longer within the bounds of traditional Christian faith. Now, I believe there is a lot of room for orthodox attitudes between the view mentioned above and biblical inerrancy (which I will someday make a case against on this blog). But my personal feeling is that, if you're going to say something in the Gospels is not true, you'd better have a darned good reason for it.
And also, it is appropriate for Christians to have a humble attitude of deference to church tradition. Obviously, church tradition has not been infallible. Mistakes have been made. But I probably will affirm the virgin conception in my statement of faith, because I don't disagree with it, and it is in the Apostle's Creed--and who the heck am I to mess with ancient church tradition? I feel it would be arrogant of me to do such a thing.