Captive bred rosy boas can have a really strong feeding response. Especially with adults, you almost never see aggression from them that's not based in a feeding response. Oddly, biting issues are pretty much non-existent with rosys from the wild, yet the first generation born in captivity can be crazy biters. That leads me to think that biting is caused by conditioning, most likely the way they are fed.
One thing that almost everyone says is that you always want to feed the snake in a separate container than it lives in, and I know some biters calm down considerably after being fed well consistently.
I would also handle it with gloves and let if chew on them for awhile so that it gets the idea that not everything is food. I've had some people tell me that wearing latex gloves can help too by decreasing the mammal smell or something.
One friend swears that leaving a dirty sock in the snakes cage can get them used to your smell and make them bite less, but I haven't heard that one from anyone else.
If it does get a good bite on you and you can't get if to release, running some water over it usually does the trick.
Oh, and there is a bright side... a biting rosy is usually a great eater!
Anyways, good luck!
Josh - rosybozo