Linux is only really polished as a server operating system, and there it is very slick and feature rich. Linux will never be anything but a bitplayer as a desktop OS, but I'm not sure why it needs to be a desktop OS.
I agree that Linux is most at home and the most feature complete as a server operating system.
And it will never be a fully polished desktop OS. Linux is developed by a lot of hobbyists. This means that it will always embrace the envelope of computing technology before the mainstream. If rocketry was cheaper, and certain limits set by the government were removed - civilian rocketry in our country would stand the world on its head with some very cool applications.
Linux will always be cool, but it isn't likely it will ever sit still long enough to become a mainstream desktop OS. Of course, we may be surprised by the adoption of Linux by a well funded company intent on turning it into a mainstream OS, and if everything I've seen is an indicator - I think it would be very profitable for a company that can use Apple's model of hardware and software synergy to add value and appeal.