Ron,
In fact, many projectors have a throw geometry with an "offset" -- meaning that, when you ceiling mount the projector without tilt, the top of the projected image will be lower than the lens center. My projector (Yamaha LPX-500, a modified clone of the Epson TW100) is one of those. So, with one of these "positive-offset" projectors, if you mount the projector so that the lens center is, say, 6.5'-7' from the floor, it is likely that you will not need to tilt the projector.
At any rate, I would avoid using the digital keystone correction if at all possible, although you may not see the image "softening" unless you watch true-HD materials.
