"The official American Atheists site says there are no ghosts and if you believe in ghosts you are not an atheist."
Sinsull, am I correct in assuming that you just threw that in for what it isn't worth? The Pope also says what all true Catholics believe, and any number of televangelists can tell you what all "true" Christians believe. I think the idea of someone officially declaring what all atheists believe is at least as much of a hoot.
I've never encountered a ghost, but I've met quite a few people who believe they have; they have, in most cases, been at least as sane and rational as I am (which may not be saying that much). None of these cases that I know as close as second-hand involve any entity or phenomenon that was in the least threatening or distructive. Those I can remember right now all appear to involve recognizable old farm folk who still show up around the "old home place".