I think it's arguable that Jim Baen changed the face of modern SF* - he certainly boosted the careers of a number of prominent authors such as David Drake, David Weber, John Ringo, and Michael Williamson (notice a common thread there?) as well as Mercedes Lackey, Lois McMaster Bujold and Elizabeth Moon. I first ran into him in my high school days when he was editing Galaxy and Worlds of If magazine. Unfortunately, Jim was too little too late, and both magazines died. Still, he'd caught my interest, and I followed his career with no little interest through his tenure at Tor Books -where he was responsible for the New Frontiers anthologies and the "There Will Be War" anthology series, which combined combat SF, science, political science articles, and occasionally poetry in a format that gave a lot of newbie authors a big boost. Later, when he moved on to found his own label at Pocket Books, I couldn't help noticing that a lot of my favorite authors happened to hit the shelves in Baen Books livery.
I dunno If I'd go so far as Quilly Mammoth in saying that Jim saved SF from the New Wave. You could probably make a good case for that argument, but as with mainstream fiction, that kind of pretentious crap tends to sink under its own weight and get pushed aside by the likes of Tom Clancy and Danielle Steel - you know, people who can actually write good plots and interesting characters without getting into the "What a clever writer am I!" syndrome. So it was with SF - although since SF is a smaller genre, you could maybe make the case that a handful of editors have an outsize effect on the field. Certainly that was the case with John W. Campbell Jr. and Ben Bova, in their day.
*Read especially Lois McMaster Bujold's essay on book distribution towards the bottom of the page, which echoes a lot of what I used to hear about this from the late Scott Imes at Uncle Hugo's.
So if you're the kind of person that prays, catch a little kneepad time for Jim. There's never enough folks like him around, and we can ill afford to lose him.