This is just another reminder that if you're writing a long message, you might want to make sure that you have the "Stay Logged In" option selected when you sign in. Otherwise you're time might run out while you're writing your post.
If you happen to forget about that and you get a login box after pressing the "Post" or "Preview" button, just hit the Back button on your browser and copy your message to Notepad or Word because after you login that message box will be blank.