I've never used x-ray film for pictorial purposes, but it looks like it could be interesting for still lifes if you can find some of the single coated stuff. The double coated materials would cause a bit of softness when exposed to visible light focused through a lens. After all, one the "back" side of the film is not in the same plane as the "front" side and that will lead to a focusing error. Granted, it's a small, but possibly significant, amount that will be exaggerated in an enlargment. Probably fine if you're confining the negatives to making contact prints.
But I noticed one thing missing in this thread that some folks might not know. The primary exposure on a piece of xray film is not made directly by the film's exposure to gamma radiation. The films are placed in holders that floresce in the presence of far smaller amounts of gamma radiation than would be otherwise needed to form the image directly. So you can think of an x-ray as a contact print. That's why a double coated piece of film doesn't loose much resolution in that application.