Jeff,
I also have Paul Hills book. He makes some good deductions about what probably doesn't propel the UFO's but he doesn't offer an answer to the propulsion problem either. He may also be wrong in eliminating a form of magnetism as the source of lift. The MRI anomolies and the Los Alamos negative gravity chamber have shown that perhaps intence magnetism may behave like gravity or negate it.
Just as we have myriads of different aircraft designs, I think so do the UFO engineers. Paul Hills' observation of the "tilt to control" maneuvers of UFO's apply to most of them but not all. The "Adamski scout ship" seen flying in a film clip featured in the video documentary "Overlords of the UFO" clearly uses this tilt to control type of maneuvering. It appears to have mass and have some sort of thrust vector. This type of propulsion does not seem to apply to the more recent Mexico City UFO though. Take a look at the MPEG in the above link. The before mentioned Adamski ship and the Mexico City ship both have that ever present gyroscopic wobble but the Mexico City saucer moves laterally without tilting. Notice the apparent lack of inertia when the disc begins to move.
The movement seems instantaneous as if the ship has no mass, yet the gyroscopic wobble would indicate it does. Perplexing.
Sean