So is it a good thing or a bad thing for MMO players? Our experience with purchasing games like Aion and Champions Online through the service has been positive, and so long as no complications arise via patches or other client issues we see no reason to stop utilizing the service unless better offers appear.
The only real MMO-related issue we can see is with collector's editions. Some games offer a different set of bonus material for people who opt out of the physical copy and go for the digital, but certain items like art books, mouse pads and other bric-a-brac can't be delivered through a wire... at least, not until sometime in the far flung future.
Now, as far as the Steamworks integration issue goes... Well, that's a whole other sack of fishes.