My DD first bit me at 14 or 15 weeks. It was excruciating and I wanted to scream, but I managed to hold it in and thank goodness I did. She started screaming...her first tooth was popping through the gum. She got her second tooth a week later and didn't get her next two until right at 6 months.
We've only had a couple of instances since the 4th month incident and I have been very careful to firmly tell her. "No biting, That hurts mommy." I hold in any screams or howls of pain. I discovered that those noises tend to make her think it's a game. (Like when she bit my upper lip when I went to give her a little kiss and she just laughed.)
A friend told me after that first bite to talk to her, she really understands more than you think, and she understands tones as well.
I still have an occasional nip from her if she drifts off to sleep while nursing in which case I just ignore it-if she's sleeping she doesn't know what she's doing. :-)
I think the important thing is to remember to watch our reaction to the initial bite, be firm, and tell the child that it hurts mommy. When she is older I'll probably have different answers to this, but now at 6 1/2 months it seems to be working for us.