When you think of how much of what we are is tied to physical properties, I just can't fathom the idea of people's experiences being geniune ghost encounters.
Think about it, people suffer brain damage that can completely change their personality or alter their senses. Everything we think, feel, and even experience is tied to our bodies. If any of our consciousness remains when the body is lifeless, I can't imagine that this presence would retain any of the memories or emotions it had during life. Those experiences die along with the body.
It seems far more likely that ghost encounters are just people imagining things or rationalizing things they can't explain. Sometimes when you experience something you can't explain, you mentally connect it with something from your past (a loved one for instance) and this could cause you to feel as if they were somehow present. It is much more likely that this is just the brain's coping mechanism, rather than a phenomenon which flies in the phase of modern science.
Just my two cents...