Me personally I have a 32-bit Mac system.
I have no fears about Apple moving to 64-bit nor do I have fears about them jettisoning PPC support.
Why?
Because Leopard is a good OS and getting better everyday. But Apple's gotta cut bait. They have to get developers on Cocoa and x64.
If you have a Mac that's 3+ years old you have every right to ask for support from the latest OS but Apple's not obligated to support these demands.
When I buy my next Mac I want it optimized from hardware to software. Apple has got to deprecate PPC, 32-bit and Carbon now. If they don't do it now they have to try to make developers and consumers do this for 10.7 which appears likely to go head to head with Windows 7.
Look at the potential timeline people.
If Apple drops a 10.6 without PPC support native 32-bit support in Spring of 09 they can shoot for a late release of 10.7 in 2010 or early 2011.
Microsoft depended on developers to be ready for Vista and MANY dropped the ball which made Microsoft look bad. Apple better drop the hammer now and deal with the aftermath.
10.6 doesn't have to have a bunch of new features. Polish what's there and add more support for iPhone and whatever other devices Apple has planned. Those that don't want to go up to 10.6 can stay on Leopard and Apple can focus on making 10.7 a phenominal leap forward and the OS that everyone migrates to quickly (new hardware purchases

)
Legacy =Baggage and baggage slows the platform down.