According to a recent article at CNET News.com,

Apple is in no rush to push out a PowerBook that would compromise the
platform’s legacy of ergonomics and portability. Were a G5 PowerBook to come out today, it would look something
like the image above. According to the article, the current G5 chip, the IBM 970FX, is just too hot and
power-hungry to make it a viable portable CPU. A new chip-making process called" strained silicon"
promises to produce a less-power-hungry G5 chip that will make a PowerBook G5 a reality.

The new process allows
the CPU’s transistors to be sped up, improving clock time without requiring more power. So, will this happen any
time soon? Most likely not, but here’s to hoping.

Explenations about the CPU can be found here
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