I'm just on this thread so I can take notes on which of the forum members are foolish enough to believe in this junk.
It's a good thing to question what is real and what is not, but if you
seriously believe in disembodied spirits of people who are
dead 
walking around on earth, you have no right asking anyone to believe anything else you say IMO.
I also think I said this the last time the topic came up on this forum, but while lots of people have those
"seen out of the corner of the eye" experiences or witness something that they *thought* was weird, to make the leap from
"I saw something weird" to
"Ghosts are real!" is just nuts.
As an expert in Fortean phenomena, (and I am), I can tell you that despite people believing in ghosts for pretty much the entire history of the human race, there has never,
ever been a single piece of good evidence that ghosts exist in any way shape or form. And you'd think after a few million years of people dying and turning into ghosts there would be at least some video, audio, or
something of all these spirits walking around.
Like most of these kinds of things ghost sightings are simple misapprehensions based on incomplete or misleading sensory data and the strong
desire to believe in them. The thing that really worries me is the folks on this thread that believe they actually saw them while
looking right at them.

It's neat, and kind of exciting to have one of these experiences and a bit of a downer to realise that they have other explanations. But if you have actually seen figures walking around in plain sight (and the guy that saw the shower curtain move all on it's own too), you are either stretching the truth of what happened a bit, or you need to lay off on the drugs, see a shrink etc.
If you want to believe in something weird, try UFO's. At least there is some incontrovertible
physical evidence that something is going on there. Ghosts? Not so much.
Seriously.