There isn't much to say that hasn't already been said about the importance of Steve Jobs. He (along with an army of talent at Apple) has quite simply changed the way we interact with the world, what personal computing actually means and how we entertain and educate ourselves. Not bad for only 56 years of life.
Jobs had a particularly distinct impact on the lives of designers. He created a revolution in design. As with all revolutions there are losers (typesetters, production artists...) and there are those that benefit. The Macintosh democratized the wold of design and while many professionals bemoan those effects, we are all the better for it. Every designer born before 1980 remembers their first experience with a Mac like it was the Kennedy assassination.
Designers' relationship to Jobs was diehard not just because we used his product every day, but because he was the living embodiment of the idea that good design driving good business. Apple has been the shining beacon on the hill. Without Steve Jobs the light is inescapably dimmer.