forgot to add on the issue of maybe leaving a link when a post is moved..great idea but I have seen this done before in other threads and usually what I noticed happening was that both threads ended up being where both threads being discussed in both threads so both threads got locked for being way off topic...

example
discussion on dissociation gets a post about dogs.
post about dogs gets moved and a link in the dissociation thread.
people see link in dissociation thread so they check out the link
and post their dissociation thoughts in the dog thread

and vice versa

now you have two threads both discussing dogs and dissociation problems. so whats going on here is this a dog thread or is this a dissociation thread. is this a dissociation thread or is this a dog thread. readers get confused, repliers get confused, both threads end up getting locked down for being off topic and possible fighting as members try to figure out each respective thread and how to post with conflicting issues in both threads.

I would rather see posts moved or deleted (and have been the recipient of both actions with my own posts) than to see the posts and threads end up being a mish mash of confusion.