I can't see Apple switching Macs back to PPC any time soon. In the last 10 years they've forced Mac developers and customers to switch to a totally different operating system AND processor architecture. Both were good moves, but it seems silly to switch back.
Apple has said they bought P.A. Semi to create custom chips for their portable devices:
They didn't switch to a different processor architecture, they switched to a system where processor architecture is insignificant, hence the universal binaries, not Intel binaries.
They could put any kind of chips in their computers and any universal application would be one recompile away from working on the new processor architecture.
That was the theory, but it's not the way things are anymore.
A whole load of stuff is being released Intel-only now. The newest PowerPC machines are now two years old, so if you're releasing something that needs a this-generation machine to run reasonably, why bother?
This proportion is only going to grow over time. And it will probably be riddled with endian bugs, alignment assumptions, and x86-only toolchains. Going back to PowerPC would be at least as traumatic as the initial switch.
Apple has said they bought P.A. Semi to create custom chips for their portable devices:
http://blogs.wsj.com/biztech/2008/04/24/jobs-still-hearts-in...