Garry's mod is probably he most popular success story of a game made by a user of Steam that saw enough success that steam came to him with a mutually beneficial plan, and he went for it. Now I don't have the full details of the GM9 acquisition, but from the way he told the story when it happened, he was exceptionally pleased and satisfied with the way it turned out.
That's not a bad thing. The Steam quality control isn't perfect--a lot of more established developers seem to be able to get games through fairly easily, but, and given my tastes in games I consider this more important, there is a remarkable lack of indie shovelware all over the place.
