Linux may go through peaks and valleys of popularity, but it will never fade away. The GPL ensures this on the legal front, and the enthusiastic Linux programming community ensures this on the technological front.
In fact, with IBM's recent billion dollar commitment to Linux research, with Mozilla finally rivaling IE in usability, stability and speed (0.9.1 is out, with 1.0 coming Real Soon Now), with Ogg Vorbis at RC1 (and 1.0 coming Real Soon Now), with the recent corporate support for the OpenOffice and Gnome projects, Linux has never been stronger as a viable desktop operating system. Linux has always been a very strong server operating system, and with Microsoft's hard-sell tactics on Windows 2000 and Windows XP, more and more businesses are turning to Linux as a cost-saving measure, ensuring stability, reliability, configurability, and backwards and future compatibility.
Jim Allchin, Craig Mundie and Steve Ballmer's Big Lie campaign (which blew up in their face terribly) shows how desperate Microsoft is in trying to combat Linux. (They called Linux unAmerican, an enemy of intellectual property, and a cancer.) Microsoft is scared. They have finally faced a competitor they cannot underprice, buy or sue.
In the words of Gandhi: "First they ignore you. Then they laugh at you. Then they fight you. Then you win."