Sometimes- mostly for young females- Headshot seems to get a reasonable approximation of the face from the front. It's generally bad at producing anything remotely resembling the correct profile, though.

For men, I have to wonder what Headshot's analysis routines are really doing- this example is just as Headshot made it, just with Image Matching turned on and opacity adjusted so you can hopefully see both, as well as the original reference photo. You can see that there is no relationship of the outer contour of the model to that of the photo. Headshot gives us smooth curves in the jaw when the reality is quite angular. The heads are not the same width, the ears are not in the correct positions, and there really isn't much that looks like the reference besides the projection of the photo onto the surface.

While it is, in its current form, a very useful tool, it could be a LOT better with some small adjustments. There's no reason that Headshot can't match silhouettes, for instance, but it doesn't even come close much of the time.
At first I thought that Headshot was looking first at the eyeballs to anchor the whole construction, and making some unfortunate assumptions about the relationship between iris size and the distance between eyeballs to decide how big to make the skull, but then I've seen several Headshots where neither of these is accurate either.
I wouldn't be surprised if the devs were secretive about the routine, but I am very curious as to how Headshot goes about its business, because things like matching silhouettes, eye placement and iris size, and jawline, should be pretty basic anchors.
Any information on how Headshot operates might be helpful in dealing with its peculiarities.