This is such a tough question and will always be a problem. There are, of course, many facets to the problem. Unfortunately, although biting is unacceptable, it is completely developmentally appropriate for toddlers to do. They are at an age where they are so smart but often lack the verbal skills to express frustration, etc. So, the automatic response often becomes biting. Another piece of the problem is that there are few things that evoke such a negative response from parents as a human bite. To parents it seems barbaric and terrible, but to a 2 year old, it seems like the right thing to do to get what you want or to deal with your frustration. In actuality, it is really no different than pushing, hitting, or hair pulling (also typical toddler responses to stress.) However, parents often get very bent out of shape about it. Also, biting hurts! It stings and often bruises and it leaves a mark, so in that respect it is tougher to deal with than a quick little push.
I have spent significant time as a lead toddler teacher and assistant director in a large childcare center. I am also a parent to 3 year old and 1 year old boys. My 3 year old bit other children a few times. One time, he bit another child on his 2nd day at a new daycare center. As a parent, I take full responsibility for this. He was not a "habitual" biter, and I was the one who stressed him out by changing his daily routine. However, I was horrified when I walked into the center to find the teacher hysterical (crying and yelling and literally pulling her own hair out) because my son had bitten another child! He did it, yes. I felt horrible for the child who was bitten and actually took care of the poor little girl myself because the teacher was so hysterical. I felt horrible for my son because he was obviously distraught in the first place. And, most of all, I felt horrible because the teacher couldn't handle a problem that was developmentally appropriate for my son to do in the first place.
Well, it all worked out in the end. Personally, I try not to get too bent out of shape about biting. I view it as the same as other "injuries" that just happen at that age. However, I do expect the daycare to handle it appropriately. I expect to be talked to at the end of the day if one of my sons bit someone or if they were bitten by another child. I expect to have a written incident report to sign if my child bit or was bitten. I expect the teachers to tell me exactly what happened and if it was a fluke or if it's becoming a problem. My son never turned into a huge biter, but if he had, I would have expected a plan (starting with observation, then separation, and progressing further if necessary) from the center. In all of my years, I have only seen one child actually removed from daycare or sent home for the day due to biting, and this child had other issues. Almost always, it can be curbed if dealt with correctly. Also, as a side note, I do believe in discussing incidents such as biting another child at home that evening. I do not, however, believe in punishment at home because in the world of a 2 year old his/her memory is so short that he/she cannot remember why she is being punished hours later and it is no longer effective.
In the meantime, it's tough to keep perspective and deal with it on a day to day basis. And, if it's being dealt with correctly, it's just as tough for the parents of the biter as it is for the parents of the bitee. Good luck and know that it is a problem everywhere that toddlers are in care. Just make sure that you have good communication. Kiss your son's poor little face...ouch!
**ETA** I am very surprised by some of the responses to this question. Biting will happen in any setting where there are two or more toddlers. Taking a child out of daycare because of a bite, accusing the daycare provider of not being good at her job, and/or saying that a child who bites has extreme issues is just ridiculous! Kids bite. That's like saying, "If a 2 year old says the word 'No' at daycare, then the parents and childcare provider are horrible," or "If a toddler says the word 'mine' or pushes another child, or takes a toy away..." That is what toddlers do! It's not a pleasant situation and it has to be dealt with but it is crazy to say that the kid/parent has issues or that the provider is inadequate. If it's not being dealt with/addressed/safely handled/communicated then that's another issue, but the fact that it happens is just that...it's a fact of life. You are a good parent, your kid is a good child, your daycare is probably a good day care!