Wow, this thread turned into a lot of absolute douchery...

Can't believe some of the childishness people are showing when they don't like what other's are saying against their one sided comments.
I've no issue with GFWL and I've never had a problem when using it, but I acknowledge that lots of people do. That said, the client is a load of faff, and doesn't give much.
I know people that bought a game on Steam want to use just Steam, it's not so simple behind the scenes. The client adds almost nothing, but the matchmaking and online play service that it uses has been tested and proven on the Xbox, and it works pretty well. More importantly, if you're releasing a game multiplatform, you've only got to implement it one less time.
If you're not going full Steamworks on the PC version of your game, you'd be mad to chop and change how your multiplayer works depending on who distributed that copy.. You can't lock people to the service they bought the game on, unless you can lock everyone to the same service. That said... GFWL wouldn't be my choice, nor any of the other existing third party ones if I could avoid it.
When it really gets confusing in why they've implemented it is something like DoW2.. SteamWorks PC exclusive title. GG THQ.