While I have confidence that dry firing is pretty safe for a 1911, I use snap caps anyway. Some handgun manufacturers, such as Beretta, say not to dry fire without snap caps, while others don't address the issue or seem to say that dry firing is ok. Everybody's got an opinion on this, but I figure if I always use snap caps, I'll always be right. I've never heard anyone say that dry firing with snap caps could have any negative effect.
Ditto on what shane said about not letting the slide slam foreward on an empty chamber. One more reason to use snap caps.