Thanks for all you guys' input. It's really helpful to know.
Although you said that it matters very little, I have to wonder how you knew that it mattered little. If a student rates you very low or lower than others on any of the questions you raised, I think the POI may change the opinions somewhat just because of this.
I would say I see it a little too odd. I agree that it's totally subjective and maybe we are just like a product to them but it's a little too cruel to do a secret rating as a host. If we knew it as an applicant, we can't be reassured totally. At least I will be very self conscious and don't feel at ease at all time until you go to bed alone. I guess although it may not matter a lot, but if it's not for money, I would really rather stay in a hotel than being judged by someone like your host. Although you can also say that you can judge them too, honestly, I won't decide not to go to a school/program just because of one person that you don't like.
I guess in general it's especially different for international students. What if we see someone who is not used to be with people different from them? I am not sure if I get my point across here but I think I particularly think one of the hosts I used to have was very judgmental about people's differences. And if I keep my mouth shut then they will say that I am too quiet.
I know different places have different people and generally they are nice but well, I have to say I don't like the secret rating system. It's like putting you into a trap. But I know...maybe we don't have the right to ask for "fairness" and I have too high of a standard.

I guess I will be satisfied with for the hosts, only report something very inappropriate instead of giving ratings of their likes or dislikes about the person. I mean...it's not necessarily reliable and it's disadvantegous for people from different cultures (especially if you happen to live with someone who is very conservative). I know there are not many international students here but I can only speak for my own experiences.