Being acontroller that works at a combined approach and tower, I run into very few pilots that DO NOT read back clearances, though lately I've been encountering a few so called professional air line pilots and our ANG F16 pilots only reading back the transponder code.
So the AIM and 7110.65 says that this is legal, is it safe, most of the time it is, but everyone should remember that old Murphy (Murphy's Law) is always lurking around, just waiting for the pilot or controller to make a mistake, so do you feel lucky?
Mike