Just my opinion, ok?
Don't make a habit of dry firing a rimfire. If you do, you'll evenyually flatten the firing pin and peen the breech end of the chamber. When this happens, you'll start having misfires because the pin will have become wide enough to no longer reliably "crush" the rim of the case (it contains the priming compound).
As for centerfire rifles, I havent dryfired mine much, but I have no fears that they'd be hurt by it.
As for pistols, I must say that most of my experience is with 1911s. I used a Springfield Armory shooting in IPSC and USPSA for several years, and practiced a lot. I KNOW that I put more than 170,000 rounds through it. I'm also pretty sure that I dry fired it in the 200,000 range, mostly in drawing from my competition holster, dropping the safety, and firing at a little orange dot on my wall (brick on the other side). When disassembling the slide for detailed cleaning, I always inspected the firing pin and never found any cracks or ring forming where the pin contacted the back of the of the firing pin hole. I did occasionally replace springs; and Wilson Shok-Buffs.
I've never read an owner's manual that advised against dryfiring (except rimfires) and if I come across one, it'd make me seriously question the quality of the gun. One company, NAA I think, actually encourages the owner to df a lot to be familliar with trigger control.
One other thing, if I had a S&W or the like with the firing pin mounted on the hammer, I wouldn't do it much. Probably should have said that on the front end of this letter.