Jeremy West wrote in with the following:
IBM just announced they have functional 110 Gigahertz chips that will be ready for market at the end of this year. No specific mention of PPC, but very interesing indeed. Imagine a 100 Gigahertz Mac by MWSF 2003.
Apparently the new chip is based on "silicon germanium chip-making":
Silicon germanium also includes layers of germanium, a substance that is like silicon but which makes a transistor that can switch faster and perform better.