As of revision 23253 you can now build his branch and have volume rendering as well.
http://lists.blender.org/pipermail/bf-blender-cvs/2009-September/022443.html
As someone who would love to see the speedier raytracer himself, can someone build his branch for Windows that includes the volume rendering? Obviously it would only be fair to have one built for Linux as well so most here can test scene rendering using his work. And of course a big thanks to Jaguarandi who did all the grunt work to overhaul the raytracer.