Funny, I never finished a post and then thought, "Oh I forgot to add the source of the words I wanted to appear were my own." I know I said this a lot lately but why don't people just try coming up with their own thoughts? Seems like some people go through a lot more work for undesired results.
I do trust both TryNinja and LoyceV but I would still argue that moderators should not use those archives to ban users, particularly if the ban reason itself no longer exists in this forum (the post has been edited by the author).
And that's why the best way to ban people for plagiarism is to just report it -- so they don't get the chance to change their post.