It's discussed in the PowerPC-forum as well.
Point is: The PowerPC-CPU that was expected for 2005 will be available in Q1 2011. Until then, Apple went from the G5 to Pentium 4 on the Developer Kit, to Core, Core-2, Core-i and will be at SandyBridge soon. The 3.6GHz Pentium 4 already smoked the 2.5GHz G5, as IBM/Freescale couldn't deliver the 3GHz G5 until the end of 2004, like Jobs said at the WWDC keynote where the PowerMac G5 was introduced - they can't even deliver it today.
The PowerPC e5500 will likely blow away any Intel, and Snow Leopard would probably still run on it (as Mac OS X was available from the start for Intel, I guess they still secretly maintain PPC compatibility, but want us to buy Intel Macs), but you won't see that, your chances are bigger to see AMD processors in the Macs, but even this is highly unlikely.