The Tango Desktop Project exists to create a consistent user experience for free and Open Source software with graphical user interfaces.
I have been using linux as my main desktop for 6 or 7 years now and I tell you that GNOME and KDE functionality are at least as good as (in my oppinion better than) MS Windows. Having a consistent visual interface could add this extra touch that makes OSS Desktops appealing to more people.
Visit the Tango Desktop Project to learn more.