I've been noticing more and more the use of that as a relative pronoun for a person. An example is, "Here is the man that opened the door for us."
I don't know for sure why that use seems to be on the rise, but I do know one thing: it's wrong!
The correct relative pronoun to use for a person is not that but who or one of its variations such as whom. Thus, correcting our example above, the sentence should read, "Here is the man who opened the door for us."
I suspect that many writers avoid who and use that in order to avoid having to decide if who is actually correct. They may wonder if whom is correct instead; unable to decide, they skirt the issue altogether by using that. The next time I get an opportunity, I'll ask.
In the meantime, use who (or whom, depending on the situation) when referring to a person and that when referring to a place or thing.