Of course I'm referring to the What you See is What you Get editor which let you see all formatting in your post as you edit it. It was immensely helpful, especially when editing, for example, threads with a lot of images. Preview post can lag a bit and just isn't as instant, so I'd really love to see the return of the WYSIWYG Editor because it was so good.
It's still there for me. Check if it hasn't changed for you via the control panel (got to Edit Options on the left, and it'll be under 'Miscellaneous Options').
You can also toggle it on and off by hitting the button on the right of the reply box (including quick reply) - the one with two A's in it with a slash through the middle. Hovering over it says 'Switch Editor Mode'.