This is excerpted from Grammar Quick and Dirty
by Mignon Fogarty - check this out and go to the link above for the rest of the story -
Today's topic is who versus that.
Lesley called in with this question:
My pet peeve is who versus that, as in “You know Bob, he's the guy that sold me my car.” It drives me nuts. Or am I mistaken and it's just become part of the new English verbiage in the evolution of the language?