I was bit by my little boa a while back, mostly because I startled him when picking him up. So I went and grabbed him anyway. Sure, it's easier to do when the snake is only 15" long and has a mouth smaller than the fingernail on my pinky, but that's what I've always heard - show them biting won't make you go away. Keep handling them anyway.
I have tried the t-shirt trick on the boa (who is otherwise a real nice little guy) and my kingsnake, and they both seem to trust me and tolerate me just fine. I don't know that they wouldn't have anyway, though, as all my snakes are docile critters. But the idea makes sense to me - they come to know your scent as part of the background, and nothing to worry about.