Get more drastic in how you punish, AND try to prevent. When he does bite, put him in his crib, take him away from his toys, or something else that really is a punishment for him (for about 1 minute). Then tell him "No Bite, you bite you no play. You nice mouth you play" or something similar.
More importantly prevent. Have a chewy avaliable. If he looks like he is going to bite someone say something like "you need to bite, lets bite a chewy" gives him something more appropriate to chew on. Even encourage him to say "chewy" to request it when he needs it, so he learns to use his words rather than a bite to get what he needs.
At one year (actually at any age), if the reaction is more fun than the consequence bad he will keep it up. Also at one, with a little perserverance you can replace the behavior with something more appropriate. If every time he attempts to bite he gets a chewy in his mouth and no other reaction, he will stop having a reason to bite.
State Certified Early Childhood Special Education Teacher
New Mom as of March 2009!