Dry firing a good quality 1911 will not hurt it. I have done it literally hundreds of thousands of times with zero damage to the firing pin (either end), or the pin hole. HOWEVER, if you have a lightened trigger pull (pretty much anything under 3 1/2 lbs), DON'T drop the slide on an empty magazine with the trigger forward. I got this warning from John Shaw in person. (He was 3time 3-gun champion, and winner of Bianchi Cup, Steele Challenge, and all the other big shoots in the late 70's and early 80's; and a contemporary with Bill Wilson, John Pride, Brian Enos, Chip McCormick, Jim Clark, and others.)
When I asked what the difference between "dropping the slide" empty vs just shooting the pistol, he explained that when you're shooting the pistol and the slide is cycling, the trigger is to the rear, and all the trigger parts (sear, hammer-engagement hook, etc) are all out of battery. When you drop the slide on an empty magazine (or no mag) and the trigger is in the ready position, the hammer, sear, and related parts can bounce around against each other. On a finely adjusted trigger group, there are only a few ten-thousanths of mating surfaces in touch, and that "bouncing around" can eat that up, ruining a good and consistant pull, or allowing the hammer to follow the slide forward. Dropping the slide (trigger forward) on a loaded mag or one with a snapcap in it, the forward velocity of the slide is slowed by the force required to strip the round from the mag, plus the force required to accelerate the stationary round.
So unless you're going to use the heavy, spring loaded snap caps; or drop the slide with the trigger pulled, I'd reccomend thumbing back the hammer for dryfire practice. Other people here may have other suggestions, but I have and will continue sticking to the advice of Mr. Shaw.