Just wondering if anyone ever built a haunted house with the arduino.... the television turns on itself.... lights go on and off randomly... doors close...sound effects and all.... would be a nice installation to safe guard your house if you are planning to go on a long vacation 
It sounds fun to do, but I'm sure my mum and dad would have something to say when I go tearing out the wires from the wall and re-witing the TV. There is always my bedroom...
Sounds possible,lights, fan, clocks, sound easy with 120 v relays. But turn on the tv I think might be moe difficult because at least my TV if I unplug it, when I plug again to power, It remains off. But maybe moding an universal remote you might be able to hide it from the others.
How about this?
Have two PIR to detect personnel. Put on in each room. If one detects person and then play some sound effect (person wispering, door closing with squeeky sound, etc) in the other room. If no person is detected in either room, don't do anything. This way an unwelcome visitor will try to check out one room and hears sound from the other room, proceeds to that room and then nothing! Just as he's wondering he hears sound from the first room. I'd be freaked out if I were him.
Make sure you're playing pranks in the room that's unoccupied so no one will ever find out the source of the sound or light effect, thus what's going on and simply choose to run away.
You can get wireless RF power controllers, to avoid too much rewiring.
I have made a beans can that jumps when you shine a laser at it. It has a motor inside the can, with an arm on it that flies up and hits the side of the can as it it was shot!