From Ben's Blog, The Bible and Culture:
...let's start with the orthodox Christian point that GOD IS NEITHER MALE NOR FEMALE IN THE DIVINE NATURE. The Bible is clear enough that God is 'spirit', not flesh and gender is always a manifestation of flesh. In the book that Laura Ice and I wrote some time ago, entitled The Shadow of the Almighty we made reasonably clear that: 1) there are plenty of both masculine and feminine images and metaphors applied to God in the Bible; 2) that interestingly enough it is not true that God is much called Father in the OT. In fact such language is rare, with almost no examples of God ever addressed as Father in the OT in prayer or entreaty, and 3) connecting such language with culture and human anthropology is a huge mistake on both sides of the ledger.
Just as it is wrong to say that the father language in the Bible is just a bad outcropping of the thinking of those who lived in an overwhelmingly patriarchal culture and couldn't help themselves, so it is also equally bad theology to suggest that the reason for the Father and King language in the Bible is because this tells us something about the divine nature or even the divine will that 'Christianity' have a masculine feel.
You can read Ben's entire post, "John Piper on Men in Ministry, and the Masculinity of Christianity," here.