What about the Emacs 22 pretests?
Emacs 22 has had several pretest releases by now, and all the major free operating systems (with the exception of SuSE) have some offerings of emacs-snapshot-gtk or similar packages.
Those snapshots/pretests are the preferred platform for AUCTeX, and in particular for W32 and MacOSX beat the pants off the "stable" Emacs 21.
But even under X11, they are in general quite more bug-free and usable than Emacs 21.
Will it run on the Hurd? Is the documentation processable with LaTeX3?