Actually, I'm not going to say much myself in this post. Instead, I am going to quote extensively from Elizabeth Johnson's Quest for the Living God, because 1) she's awesome and 2) she makes a really nice shield.
Johnson offers three basic ground rules for engaging in God-talk, that is to say, doing theology (whether one does theology professionally, or personally, or in my case, both). 1) remember that "the reality of the living God is an ineffable mystery beyond all telling;" 2) therefore, "no expression for God can be taken literally. None;" 3) Therefore, "from this, Thomas Aquinas argues...we see the necessity of giving to God many names" (Johnson 17-22).
Applying these reminders for our God-talk specifically to the issue of God's presumed maleness, we get this: 1) God is beyond our socio-linguistic categories, including that of gender; 2) no pronoun (male, female or neuter) in reference to God can be taken literally; 3) we need ways to reference God that incorporate every possible category since they all equally apply/do not apply.
Johnson herself observes this regarding the univocal, historical, traditional maleness of Christian God-talk:
"the practice of naming God exclusively in the image of powerful men has had at least three pernicious effects. First, because it offers no alternatives, it gets taken literally. Thereby it reduces the living God to an idol. Exclusively male language leads us to forget the incomprehensibility of holy mystery and instead reduces the living God to the fantasy of the infinitely ruling man...Second, in addition to this theological error, the exclusive use of patriarchal language for God also has powerful social effects...In the name of the King of Kings and the Lord of Lords, men have assumed the duty to command and control, exercising authority on earth as it is in heaven...Third, by giving rise to the unwarranted idea that maleness has more in common with divinity than femaleness, exclusively male images imply that women are somehow less like unto God...a woman may see herself as created in the image of God only by abstracting herself from her concrete bodiliness...Thus is set up a largely uinconscious dynamic that alienates women from their own spiritual power at the same time that it reinforces dependence on male authorities to act as intermediaries for them with God" (Johnson 98-99).
Johnson goes on to discuss the wealth of biblical imagery of Mother God, only one among many female images of God in the biblical text.
But I want to emphasize her main point, which I will paraphrase thus: insisting that God is male reduces God to the image of man. And God is not a man.