Ubuntu and SuSE are definately gaining ground. Google is currently over 50% Linux, using a google customized version of Ubuntu called "Goobuntu" for the most part, with some other distros thrown in for good measure.
IMHO, Windows has already peaked long ago, and it wasn't WinXP, it was Windows 2000 Professional.
Dan still uses it, and I really do believe that its still the best Windows ever made, featuring the first of the NT5 kernels, but without the rubbish and crud that Windows XP was full of.
Thing is when the Pentium 3 was ultimately defeated by the Athlon, and Intel had to take up a new direction, they chose Netburst, and built the Pentium 4 around it. Although they did their best, Netburst was never that practical on the desktop, and at some point they accepted this. Their new product, that has taken the company from catching up, to leading, is not a new technology, but a vastly improved old one.
At the heart of every Conroe, is a Pentium 3. A Pentium 3 on steroids, with a great deal of enhancement, but a Pentium 3 none the less.
Microsoft needs to go back and look at what they've done well. Then build on it, rather than throwing out the cookbook.