I personally don't belive in ghosts, the simplest solution is often the correct one. Until I see solid evidence (read; a ghost directly in front of me) than there's very, very little chance of me beliving in them. creaking and groaning in houses is the natural movement of the structure, scratching noises are caused by small anCmals, and visual effects are tricks of the mind or light.
I'm not saying you can't all belive in them, i'm just saying I never will.