See this discussion:
http://superuser.com/questions/343572/how-do-i-reorder-tmux-...
It kind of works in the end, but it's arguably a bit more awkward to use than in screen.
Your right, I remember that discussion: I actually use pier solution, with the shellscript (I assigned them to Ctrl-A + Number)
I agree that it does not work 'out of the box', but once setup, it works quite nice :)
What do you mean? Commands like tmux swap-window and tmux move window allow you do move the order of the windows / workspaces.