Leave it to Microsoft to not promote their next major update for their Games For Windows Live clients. However the 3.0 version of the PC gaming service is indeed now available for download at Microsoft's web site (there's no auto-update available as of the time of this post).
Aside from a brand new color scheme and art style there's not much that's been changed in the stand alone client's user interface. However, posts on the Games For Windows message boards indicate the in-game client for Games For Windows Live does have some new features such as being able to add Microsoft Points in the game itself to purchase add-on items. You can even change your GamerTag for a "mere" 800 points.