I'm not saying there aren't ghosts, but I'd say at least 99% of most "witness" accounts can be explained. For instance, a big one on Ghost Hunters is people feeling like they've been grabbed. I've had spasms in my shoulder and back that straight felt like someone grabbed me. I admit it shocked me when it happened but that's what it was.
The only experience I've had that I even remotely consider "legit" is an episode of sleep paralysis where for about 10 seconds I "watched" myself sleep and was able to see my wife in the next room reading a book. I saw what was on TV and what time it was on the wall. That kind of creeps me out, but even that I could it was a dream/hallucination where my mind projected what was going on around me and did a really good job of creating it. And that wasn't even a ghost sighting.