I personally don't think that black holes move faster than light. I mean, all they really are are collapsed giant stars. I can understand how a black hole could be moving pretty fast providing the star it collapsed from was also moving pretty fast, but I've never heard of a star that can move faster than light. Maybee if you could list the particular book you got imaginary time out of, I could see what you're saying. But the only way time could affect the speed of the black hole, I think, is to somebody inside it. If the black hole was moving, say away from earth towards M31, it would get there less than instantaneously to the persective of someone inside the black hole, since time is so warped. But to a person sitting n earth, the hole would still take many, many years to reach it, even if it were moving close to the speed of light. I've read about all the effects of traveling near the speed of light, and I remember it being said that it was impossible to cross that "barrier", if you will. A person standing on earth can never accelerate beyond the speed of light. Likewise, the theoretical tachyons, should they exist, could never decelerate to below the speed of light. (tachyons are theoretical particles that are thought, if they exist at all, to travel faster than light. But they could never decelerate to the speed of light or below, just as you or I couldn't accelerate past the same limit.) Perhaps the imaginary time theory you said was in one of Hawking's books could shed new light on the matter, but i don't see how yet.