This happenend to me and two other witnesses at Happy Valley in Adelaide, South Australia one very stormy night in 2003. My two friends and I were talking and watching a movie when their pet dog, who was shut outside, started to whine and carry on. There was quite a bit of thunder and lighting, so we didn't pay much attention.
All of a sudden, out of the corner of my eye I saw a movement in the hallway. When I turned to get a better view of what was in the hall, I saw a jet-black, human-shaped and -sized shadow. Both of my friends turned to see what I was looking at and they saw saw the shadow being as I did.
As it passed behind where we were sitting, there was a very loud clap of thunder. We heard the sliding door open and then their dog shot through into the room, which was odd due to the fact that the door was shut and locked. When I got up and checked, I discoverd that the door was still shut and locked!
I learned later on that a previous tenant of the house was witness to a violent crime and that he later died of cancer. All in all it was quite an exciting expireance.