I'd say that Steamworks is slightly worrying, as it's one more stop towards monopoly central, however that's the ONLY complaint I have about Steam. (OK one more, sometimes the prices are a bit high compared with Amazon's boxed retail version.)
Even the forced ads that pop up, half the time they're informing me about a weekend end deal I'm actually interested in, or a new release indie game that I'd never have heard of. Steam, while of course it pushes the big games, also bothers to push the small dev indie stuff in a way that I can't see say, Amazon putting 'Undergarden' on its PC front page.
So long as Steamworks doesn't get too much of a hold on the market, I'm very happy with Steam, but Steamworks does stop other DD companies selling that game, therefore I'm against that, because of the need for competition.