Getting a little carried away with AutoPano Giga... it's a beautiful piece of software. All of the frustrations that I've previously had with stitching panoramas (getting the right projection, angle of view, control points, etc) don't appear to be an issue here.
As a stress test, I attempted to stitch all the frames I had of both the Scorpius and Orion halves of the Milky Way. The end result is
HERE.
My favourite feature: it's trivially easy to switch between straight-horizon and straight-Milky Way projections.