GNU/Linux for the desktop is to challenge other OSs, to the point where we can *FINALLY* have some open-standards, everywhere. I don't care if OSX and Windows and Solaris stay mostly proprietary and in larger shares (Eg, 30%+ of total market) as long as we can openly communicate with them. At least that's how users view it, and with OSS, users control it.
Linux on the server? World domination. Really, that's all their is to it.