Definately believe. My parents have had a lot of things happen to them, things that they have witnessed individually and also together, and some pretty creepy stuff at that. The only thing I witnessed while living in my home growing up was the water in the bathroom sink turned on full blast with nobody in the room. We had company over, and they were REALLY freaked out about it.
My parents believe that I have some sort of guardian angel watching over m.e They claim that when I was less than a year old, they were in bed (and I was in a crib in my room) and they heard someone talking in my room. They freaked out, ran into my room, and saw me sitting up staring at a corner of the room (not scared or crying or anything, just staring). Apparantly I was very interested in that corner for many days/weeks afterwards.
As I said, my parents have dozens of stories to tell, and some are pretty freaky.
CW