In old photo cameras — you know, the ones with film — you have to concentrate on every shot, every frame, because you paid for some 24 exposures, and there are no do-overs. But today's digital cameras are an endless blank slate, where the number of shots you can take seem limitless and mistakes are erased with a click. And they continue to become more practical, convenient and awesome, especially the new iPhone 4 (with a built-in flash) and the new Nikon Coolpix S1100pj, which includes a projector that allows you to view life-size images and video on a wall. Gone are the days of hearing the film rewind into its casing, transporting it to a photo lab and patiently waiting to find out how amateurish your snapshots look. In this instance, the present definitely trumps the past.