Why does my saved CMYK image appear dull in preview programs, and will this impact the final printing?

It probably is an artifact of the conversion to RGB, though since it has already been through the reverse transformation, it's possible that the image has been degraded. If you haven't already, you probably want to color-calibrate your monitor to make certain the image that you are viewing is displayed in true color. ( a href="http://en.wikipedia.org/wiki/Color_calibration" rel="nofollow"http://en.wikipedia.org/wiki/Color_calib…/a ) Other than that, you should definitely have a test print made, as that is the only way to be absolutely certain that it will look the same when printed as you actually wanted.