@okie,
Hi Okie,
Dont know if someone else also already explained this (sorry if so), but from what I understand:
-> If you vote down a post, it disappears for you, but others can still see it.
-> Also, it doesnt disappear entirely -- it just "collapses". You can still see that there is a post, you just can't see the post itself. It will say in tiny letters, "Post voted down (view)", and if you click View, there it will be again (handy if you accidentally vote a post down).
-> Finally, I think if enough readers vote a post down, it becomes collapsed by default for everyone - but even then curious people can still click view and see it after all.