If your cat bites you hard (not play biting), slap him around the face, with 2 fingers. Do it immediately, so that he knows exactly why he is being reprimanded. You can also make a loud noise when he bites. This further reinforces the idea that his action is hurting you.
Had the cat been with its mother, if he got out of line, he would've received a similar slap around his muzzle, by his mother.
If you don't discipline these animals at a young age, they will grow up to scratch and bite humans - something which I think is unacceptable. At an older age, when they bite/scratch, it will be a lot more painful.
Discipline is VERY important and it is unfortunate that most pet owners have no idea about this.