I've gotten gifts from roughly half the prospective students I've hosted over the years, and I gave something when I applied. I think it's a nice gesture of appreciation, but by no means does it have any effect on someone getting into the program or not. The gifts are usually something small, like a small box of chocolates, or a jar of jam, or some vermont maple syrup (that was cute, since the person was from Vermont).
Much more important than a gift is sending or leaving a thank you note with the person who hosted you. I mean, if it's similar to my program, I'm picking someone up at the airport driving someone around for 2 days, having them sleep in my apartment (and I usually give them my bed, since that's more comfy than my couch), try to get a variety of breakfast and snack foods for them, bring enough alcohol to the student party for the both of us, and try to generally be helpful. I'm happy to do it, and return the favor that people did for me at the time. But, while students are encouraged to host, it's not required and it is a fairly large imposition on someone. So, I think it's good to be gracious that they're hosting and not making you pay for a hotel. There's only one person who didn't write a thank you note to whom I've hosted, and I have to say that did annoy me. I do think it corresponded with a general lack of social skills on that person's part, and they didn't get in for reasons relating to those social skill deficits.
Just my 2 cents!