lowyhong: Gamersgate is great. It is the only other digital distributor that I rank about the same level as GOG (am quite indifferent between the two). Their Blue Coins system is superb and a very nice reward system for long-term customers. And their tech support is just as friendly (and more responsive) than GOG's.
As far as I'm concerned, if GOG want to set their sights on Steam then Gamersgate is the one they really should be competing with. Gamersgate's support, features and ability to encourage users to help one another and provide reviews, ratings and even walkthroughs places their level of service above all else.
GOG has the more solid foundation of (somewhat) guaranteed compatibility and, of course being DRM and region free. That's not something that any other existing service can hope to implement. Apart from perhaps DotEmu, but GOG don't have to worry too much about them.
GOG have got a long way to climb in terms of adequate speed and consistency of service, adequate coverage of technical support and then there are the bugs...