Believe only what you see?

Tonight was a very interesting night for me. I went to a friend's house to make Chex Mix and hang out with her and her mom. We were sitting around while the mix was in the oven and we started talking about her living alone and all the ups and downs that come with it. Well we started talking about her feeling safe and she started to tell me about her friend, Pete that lives with her. Now I was really confused because I knew she lived alone. And then she started telling me about different things that Pete would do. And soon after that I realized that Pete was not a person but a spirit. Now I have to tell you that this subject has always made me uneasy but I do believe in spirits completely.
She told me about lights that would be on when she had turned them off, her christmas tree being plugged in and lit up when she got home from work, "feeling" him when she walked by him in the house, and hearing different noises that she knew she wasnt making. It was very creepy to me and I am just glad that nothing like this happens in my house. It is interesting to me to hear stories about people and their experiences with spirits...Anybody got any good ones? Or do you even believe in this?